The CR can be equal to your character level. That's a little nuts. I don't see how you could even do that beyond 3rd level, though, unless you use some template like Grave-touched Ghoul. A ghast only has a CR of 3. Without resorting to templates, it seems like kind of a waste of a feat...
Assuming we're only talking about standard ghouls and ghasts, I'll say they have separate pools. If not, we'll have to talk about it more... 
There's a Tome Ghoul much like the Tome Vampire. There is a degree of diminishing returns in taking multiple necromancy feats, in that it takes a move action to give a command to a single minion. So, even with three move actions it would take three turns to get the whole crew into a battle. Having eight to send in the first place is pretty nasty. But if the encounters are likely to be such that changes in orders will often be necessary, maybe it would be OK to have separate pools? The CR=7 thing should, of course, be right out.
Ah, I forgot that, and I'd overlooked the Move action to issue commands. You could still issue "generic" commands like "guard me" beforehand though, since they are intelligent and can understand complex instructions. So if you're clever about it, it won't take much effort to get them into action. Ok... I see that you really want an army of undead slaves... So let's assume the CR for the ghouls is also your CR-2, and make it separate pools I guess... I'll just have to throw more fodder into the encounters. More work for me.
You know, that cloaker minion made me look at the thing's stat block. Why not use it as an actual cloak and have it absorb half the damage from every attack? 
For style points I'm thinking of a vampire who has an undead cloaker with the swarm-shifter (bat swarm) template. 
(I've seen batcloaks at least twice now...)
That's... a freakin' awesome idea. Hell... maybe you should have a bunch of your undead minions be cloakers so you can "outfit" the rest of the party with them.
They're great monsters anyway, with a flight speed and crowd control abilities.
Since you technically have to be "engulfed" by the thing for it to absorb half damage, I'd say the cloaker would have to ready an action to engulf you just before you were attacked. It could then release you from the grapple at the end of its turn (at its new initiative). So it would probably at most protect you from a few attacks from one creature (or several if they all have the same initiative).
Also, I don't know if you put down any Black Sand on your character sheet, but I have no problem with you having some to heal your minions with out of combat. I think my affinity for necromancers is showing... I'll try not to unfairly favor Xuuvosic... too much.
I certainly won't be pulling any punches at all with your minions, though. Since they're free to make, expect me to treat them like Star Trek "Redshirts".
Awww.... hell! You could even have the Cloaker carry you around in its mouth, and you'd have a huge wavy cloak that lets you fly! Like motherfuckin' Spawn!
