Hi!
regarding the Horse Archers and the Dire Wolves, maybe you'd like to use something with a bit more combo potential, like your Ghouls with your Strigoi Ghoul King and your Crypt Horrors, for a Flesh Eater army, since synergy works best in AoS.
Also, you may want to get a generic Vampire Lord if you plan to use a lot of different non-combo units (just as you are suggesting), so you can use "cheesy" units that function more or less independently, like Vargheists (no current specific bonus applies to them, unlike Varghulf which is also a Flesh Eater, so Vampire Lord's Blood Feast clicks with them).
The Casket of Souls does combo better with Liche Priests, but it functions very well on it's own, so I agree on that one. Maybe I'd throw (if you could spare) a Necrotect to get double shots from the Catapult, although if you are planning on fielding it, you may want to consider providing it with some sort of guard to keep it shooting and unengaged for as long as you can, since it can fire upon almost anything anywhere on the field (in this case, enemy units around your target terrain).
You have fast very very mobile units with Sepulchral Stalkers, Vargheists and Morghast Harbingers (if you have Archai, I'd recomend putting them on guard duty along the Necromancer instead, since his Undead Minions's special rule ignores a wound but causes a Mortal Wound instead, and Archai's Ebon-wrought Armor has a chance to ignore said wound, making them an obvious combo). You should get some staying power to control the objective OR ignore the game's objective and hunt stuff down and kill them as efficiently as possible, with the use of Sepulchral Stalker's ranged attack, Catapult's and finishing off with a charge from Vargheists/Harbingers buffed with the Vampire Lord's command ability. You could win just by removing big threats and then burrowing -> unburrowing your Stalkers inside the terrain you need to control to leech some points before engaging other units.
It's a gamble, wether to build a strong army that must move close to itself, but you'd have to leave the Catapult out (or be willing to lose it early on without support) so you can control the objective for as long as you can, therefore requiring as much Reanimation as you can get, plus banners plus aoe buffs like a Wight King's Infernal Sandard and more infantry; OR build a mobile army that can strike hard and fast at few but crucial units, but will not be able to hold the terrain and could have some problems against clustered units that can sacrifice the frontline to keep your mobile units engaged and grind them down via attrition.
Either way you are faced with a problem, so... how do you like to play the most? =D