I would hope that we could get fire magic from the fire plane if we need it, while fire-attributed minions are likely to be very weak in the water plane, potentially self-explosive in the air plane, and somewhat bad at working with others on the material and earth pane due to collateral and insulation reasons respectively. I certainly want an "in" with magic, but I feel that the Lich gives a better starting-point, and plagues and rot ought to fall loosely under the scope of necromancy and curses and can achieve much the same as fire can, while for fire to replicate necromancy and curses it will likely need to create fire creatures and mess with the humours? I guess we could try to get earth magic from the earth plane to try to balance out our imps...
Unholy and Archdevil have a nice theme going, but seem a bit redundant in terms of knowledge, both being demonic, and I don't really see berserk working so well for the small and clever imps. Of course, we can make more suitable demons to work alongside the archdevil, so it isn't that bad.
But still, my biggest concern is that we will get a bad combination. I feel that berserk probably doesn't work so well with things that are already mindless. They will probably become more energetic and stronger, but most of the classical advantages of berserk were associated with ignoring injuries and imminent death, which is already there. And I would love the double-whammy of magic from both lich and unholy, but the imps would gain very little from the leadership. Granted, we can make emotional hordes and stupid demons to go along with our champions. Or probably modify our champions into providing a more magical frienzy that lets them keep fighting for a while after being completely dismembered and decapitated or an intelligence bonus that focuses more on strategy and logistics and less on reminding people that pits with spikes in them are not trampolines.
So... I guess it will work out whatever?