Strengths:
Skeleton production
Vampire Lords with their regeneration

Weaknesses:
Ghost Dragons being not any strong in combat.

Army evaluation:
Skeletons 5/4/6/1-3/4/60
Skeleton warriors 6/6/6/1-3/5/70
Their strength lies in numbers, not their stats.

Walking Dead 5/5/15/2-3/3/100
Zombies 5/5/20/2-3/4/125, cause disease (-2 A/D for three rounds)
Almost useless, their role lies mostly in castle defending.

Wights 7/7/18/3-5/5/200, regenerate
Wraiths 7/7/18/3-5/7/230, regenerate, drain 2 spell points per turn
Flyers of average speed, their use is in castle sieging and in eliminating4 weak shooters. I rarely use them, though.

Vampires 10/9/30/5-8/6/360, no retalitation
Vampire Lords 10/10/40/5-8/9/500, no retalitation, ressurect by damaging enemies
In their resurrecting version, they make a good castle sieger. In high numbers, they're very hard to beat down. Note that the regeneration doesn't work if vampires attack non-living enemies (undead, golems, gargoyles...)

Liches 13/10/30/11-13/6/550, area damage to living
Power Liches 13/10/40/11-15/7/600, area damage to living
Offensive stats, good speed and area attack make them a good sieging weapon.

Black knights 16/16/120/15-30/7/1200, curse enemies
Dread knights 18/18/120/15-30/9/1500, curse enemies, deathblows cause double damage
They're more than a match for champions - mainstay of offensive forces.

Bone dragons 17/15/150/25-50/9/1800, lower morale
Ghost dragons 19/17/200/25-50/14/3000 + 1m, lower morale, aging attack halves HPs of enemy
Although not very strong, their upgraded version is very useful in battles due to speed. Their special is quite dangerous, too.

Upgrading priorities:

• Skeleton Warriors: Low. Although used often, their performance isn't crucial.
• Zombies: Lowest, they are rarely used for offensive purposes
• Wraights: Moderate, the speed boost allows then to cross battlefield sooner.
• Vampire Lords: Highest, dramatically prolongs their lifetime.
• Power Liches: Moderate. It would be high, but they're way too often targeted by castle towers.
• Death Knights: Higher for speed boost and destructive special.
• Ghost Dragons: High for large battles with strong armies, generally a good upgrade for the speed boost - can reach most enemies as well as flee from them.

Castle building in the first week:

Day 1:	Town Hall	2500g
Day 2:	Graveyard	1000g + 5o
Day 3:	Estate	2000g + 5w + 5o
Day 4:	Mage Guild	2000 g + 5w + 5o
Day 5a:	Mausoleum	2000g + 10o + 10s
Day 6a:	Hall of Darkness	6000g + 10w + 10o
Day 5b:	Necromancy Amplifier	1000g
Day 6b:	Tomb of Souls	1500g + 5w + 5o
Day 7:	Citadel	2500g + 5o

Cursed Temple as 1stlevel dwelling assumed present. If it's not present, we choose the b) variant without Tomb of Souls.
The a) variant requires a lot of money - use it if you have a stable gold source (a mine or a village).
The b) variant is aimed at getting Upgraded Estate on day1 week2.

Resource summary:
For a) variant, you'll need 20w, 40o and 18000g, which leaves us (20000 + 7000 - 18000) = 9000g for Day 1 to spend on troops. This could be 5x1200 for Black Knights and the remaining 3000 could be used for 5 liches (but I would rather save that money for City Hall)
For b) variant, you'll need 15w + 25o and 12500g. If you can't get the +5 ore, buy any benefit building instead of Tomb of Souls (Citadel is more important that Wights). And remember to include another 5 wood for upgrade of Estate on day1. Thus, you'll have 12500g for troops - which should easily pay for 10 Vampire Lords (10x500) and all available skeletons, while enough money should remain so that you can build City Hall, Mausoleum and Hall of Darkness within the second week (although you'll need some extra wood and ore by then.) With some luck, castle might be raised on day7, week2, capitol at least 5 days later and into the third week you could go with a pretty strong army.

Second week strategies:
The b) variant is mentioned above, the a) variant should get a CityHall ASAP and then head for Castle, Capitol and some upgrades. With some luck (and resources) you could be able to build Dragon Vault - so plan carefully - the extra dragon or two could prove more valuable than Castle/Capitol - so check the resources needed for the Vault. The Tomb of Souls doesn't have to be built at all - and the 5w and 5o might be needed elsewhere.

Troops cost weekly (with castle):
Without 7th level: 20920
With 7th level: 26920
With one castle producing 14000/week, you sure will adopt the policy of ignoring wights, zombies and even skeletons in order to get your only ranged attacker and two massive damage dealers... Capitol at 28000/week will change things around and start growing money.
HPs grown weekly 1792 (plus 400 in ghost dragons) at 11.67 g/HP (12.28)

Benefits:

• Blacksmith: First Aid Tents sold here... Strange, ain't it?
• Cover of Darkness: Generates shroud around city every turn - good for concealing your activities, but if I were you, I wouldn't build it before my enemies KNOW about my city - if their scouts uncover a bit of the affected area and next turn it is darkened again, they'll learn of your city's approximate location. Also, I'm not sure how this works against computer.
• Necromancy Amplifier: A must - 10% necromancy boost.
• Resource Silo: +1w and +1o per turn
• Skeleton Transformer: A nice idea of disposing armies that offer to join. Why get less than 100% skeletons? ;-)
• Unearthed graves: Increases skeleton growth by 6 - buy soon or never.

Strategy
In a) variant, ore is crucial. You have four days to determine which variant will you choose. Wood is crucial in second week, no doubt.
Don't ever hope to buy all the troops that you'd like to - you'll need a good gold source for a decent number of days to get enough...

Forces combination:
I suggest Vampire Lords, Dread Knights, Power Liches and skeletons.
Later, when you get the Ghost Dragons, you might make a special force of them and skeletons alone, possibly also accompanied with Wraiths that may have been unused till this time due to lack of gold. Wraiths divided into several stacks are a great choice - having one skeleton stack, one or two dragons and four wraith armies, best split to 1,1,1,rest works great. The enemy will either lose loads of mana or spend a lot of effort on killing a single wraith three times. (One wraith will drain as much mana as a hundred.)
The wraiths in the above combination are used as a cleaning force, but sometimes you might sacrifice them to save the dragons.
In the beginning, you'll be limited by money greatly - and it's better to pick only two from the three strong troops and stick to them. If you can, don't leave the liches home. In earlier phases, their offensive potential is great - definitely better that potential of Vampire Lords (until their number tops 20 at least).
Upgrade to skeleton warriors only when you get dragons - skeleton warriors are raised like skeletons, but you have to have all slots occupied and no normal skeletons present - so the ideal setup is two stacks of Dread Knights, two stacks of Power Liches, one stack of Vampire Lords, Dragons and skeleton warriors.
Yet you can split the Liches/Knights into more stacks.
Later you might split skeletons and have either knights or liches together, depending on individual situations.
IMHO 66 skel. warriors are better than 100 skeletons - the +1 speed gives you enough first strikes to compensate the lower numbers.
Alternative to that can be amassing skeletons and every now and then using a scout to take some 100s of skellies home and upgrade them.
When using Liches, watch out for war machines on enemy side. They can be targeted and if six or less army slots are filled on the enemy's side, aiming at a war machine causes TWO adjacent armies to get hit.
Huge stacks of Vampire Lords should be used cautiously, mixing their targets - one round go attack something strong to cause non-retaliated damage. Second round - go replenish yourself at something with low defense rating, typically shooters to block them as a by-product.
Critical to your strategy is the rule 'all that moves can be killed'. However, things are not as easy now as were back in HOMM2 - now the wandering armies will go after your skeletons and therefore the skeleton 'gain' may actually be a loss - be careful when messing with wandering armies of 4thlevel and higher creatures.
Also, if you rely on skeletons, try hard to get Vial of Life or either one of the rings that increase HPs... Skellies profit from them greatly.
Covenant suggests using always one might and one magic hero (preferrably Galthran (skeletons) and Thant (Raise dead)) and let them share the experience from slaying armies. The good thing here is that the might hero can be used against all weaker units, where he profits greatly from his A/D ratings, while the magic hero can tackle stronger wandering armies, compensating losses with Animate Dead.
Also, it's a good idea to obtain Scholar skill for some scout so that Animate Dead can be passed from Thant to all your heroes (in case you didn't get it in some guild).
With Earth magic, it's worth it to use Shield on skeletons, since they're gonna be targeted by most enemies, esp. AI.

Heroes:
Death Knights: Try to get Galthran if you want to rely on skeletons, since the +1 speed on them can be a crucial point, not mentioning A/D bonuses. Isra is a good starting pick with advanced necromancy and 5% bonus to it. Tamika (offense, knights) or Vokial (artillery, vampires) are useful. Moander (liches, learning) is not that great, learning is a wasted slot. Yet any of the might folks that sports one of crucial unit does a good job - the +1 speed decides many battles. Clavius (350 gold) is a good secondary.
Among Necromancers, good are Aislinn (Meteor Shower), Sandro (Sorcery), Vidomina (adv. necro + 5%), Xsi (Stoneskin, learning), and the all around popular Thant. Others don't seem any good to me.

Skills important for the troops and strategy:
None are exactly needed, but I recommend Earth Magic for Animate Dead and Death Ripple. Air magic should be useful with Haste, best combined with Tactics. Fire magic is another good choice - for Blinding, BloodLust and area spells. Also Curse is handy to counter Bless ;-). Water magic seems most useless, yet I think that Clone/Prayer/Teleport/Dispel aren't really bad spells and apart from the first one, they're mass versions with Expert. [counting the needed skills, we have Necromancy, Logistics, Earth Magic, Wisdom. The other four places could be used for the following: Tactics, Ballistics, Diplomacy (to get free bones) and Air/Fire/Intelligence.]

Unit	A	D	HP	Dmg	Sp	$$	AdjD	Dm/g	grow	weekD
Skeleton warriors	6	6	6	1-3	5	70	1.84	2.63	30	55
Zombies	5	5	20	2-3	4	125	2.25	1.80	16	36
Wraiths	7	7	18	3-5	7	230	3.76	1.63	14	53
Vampire Lords	10	10	40	5-8	9	500	6.50	1.30	8	52
Power Liches	13	10	40	11-15	7	600	14.95	2.49	6	90
Dread knights	18	18	120	15-30	9	1500	31.50	2.10	4	126
Ghost dragons	19	17	200	25-50	14	3000	54.38	1.81	2	109