Yeah, let's just max out the two Knowledges, Spot, Listen, and Intimidate. That gives a line of
Intimidate +19, Knowledge (religion) +15, Knowledge (the planes) +15, Listen +17, Spot +17, Survival +5 (on other planes) .
Look ok?
Let's go for Imp Sunder as the last feat.
To fill in a few more question marks:
LA: -
Treasure: None
Hmm, I was thinking about the org and then noticed something. Don't we need to specify somewhere how many minions a master "starts with"?
I'm happy to keep them with 6 minions to start but allowing the minions to advance along with the master (time for an underbar, methinks). But we should either mention that number 6 in the background or the Minion Dependence SQ or both.
A related question is if we're putting them into the same CC entry or two linked ones. I guess with linking, it doesn't make too much of a difference.
From looking at the original monster, it seems we should note that the Minions get banished back to the 9 Hells if the Master is destroyed. Seems like that would fit in Minion Bond. Or did we decide to drop that?
The original monster Masters always seemed to have 6 minions, so I guess we should stick to that. But maybe the Minions should gain 1 HD per every 3 or 4 HD the Master gains in advancment. I don't think I'd necessarily have the Masters change size, but HD advancement up to maybe 22 HD would work.
I like a two-to-one ratio, since that'd mean the Minions and Master's BAB and good saves increase in time with each other.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.