Prestige class and base class interaction (Undead Lord / Agent of the Grave)

[yumad]

Need a bit of clarification on how these classes interact with each other and what cleric abilities scale with Agent of the Grave levels and which don't.

I assume that you don't gain the actual cleric bonuses like the level 8 Undead Lord negative healing bonus until the Undead Lord class hits level 8 but what about things like:

Command Undead channel? Do you only have your cleric levels worth of HD to control instead of having cleric levels plus every Agent of the Grave level save the first bringing that up to 9HD at 5 Undead Lord/5 Agent of the Grave?

The save of Command Undead channel is DC 10 + 1/2 cleric level + CHA, would this "cleric level" be unaffected by Agent of the Grave spell casting level increases?

Corpse Companion, this one I assume is not affected by Agent of the Grave it seems fairly discrete but it's good to ask anyway.

If the Agent of the Grave prestige class spell caster increases do not affect these abilities then it does not seem like a very useful prestige class for intelligent undead use, only hordes of mindless undead which can get unpopular at the table when your turns take too long.

Edit: Also as an aside but slightly relevant, Command Undead channel has a maximum number of controlled undead equal to the stated HD right? Or is that per cast with unlimited amount you can control as long as they don't will save?

[Weirdo]

The only features that stack are features that specifically say they stack - in this case, it's only your spellcasting. It does look to me like a pretty poor prestige class for a cleric who wants to control undead.

Command Undead has an overall maximum HD, not a maximum per use.

[yumad]

Well Agent of the Grave does offer increased amounts of HD for animate dead, all raised dead are considered raised in desecrate and they have a spell-like desecrate available as well as a host of other useful things, it just hinders intelligent undead use.

Are you certain that the spell DC for command undead would not increase? That seems like something that would go up because you gain effective spell casting levels from the agent of the grave class for your class of choice.