they NEED some sort of armour with protection zero, other than that dress for the occaission, a good sheild help but isn't vital aslong as you make use of that flight and kill archers/crossbowmen fast.
also you asked about putting some mortal troops with them, i say no just reserach blood rite, it's a blood spell (duh) which you're counts can cast with no boosters, for 22 blood slaves it gives you 8+ vampires (vampire units not counts) yeah you may want to spend slaves on counts and such but once you have a few counts out you can make good use of this, by late game you should have hordes of immortal vampire legions and vampire counts blood hunting all over your dominion, no need for cash because you are summoning immortal troops and mages (vampires of the leader and unit variety).
also good to add is that none of the vampires have an upkeep cost - again a reason why you don't need cash, blood slaves should replace both cash and resources for you if you put enough drive into the vamps,
and the best thing is you WILL have an endless horde of troops, because no matter how many die (so long as they die in you're dominion) they will all respawn at you're capital ready to be dispatched against the next enemy force to wander into you're dominion.
Perhaps you're dominion will be feared as much as ermors, just turn taxes up sky high - scorched earth style, and you won't be at any loss (though it makes blood hunting harder but still you're troops respawn themselves after death so the enemy will just keep getting weaker whilst you get stronger or at the very least stay exactly the same)
The only sad part is ulm isn't amazing early on (except the crossbowmen - love them) but once a few counts are out and yuo have a decent blood economy it does look up and only gets better
