[Valerius]

There's no getting around the fact that you'll need your cap for immortal units to return to and to recall your pretender if he's killed, but other than that I'd say it should be de-emphasized. Meaning no really important (if any) cap-only units. Of course having very powerful recruit-everywhere units is a balance issue (assuming you care about that aspect) so it would probably be best to make those powerful units summons. Also, inquisitor seems thematic, maybe even blood sacrifice depending on the magic paths. So they can very quickly push their dominion and get a foothold in different areas of the map. I think old age being an issue for the oldest and most powerful members of the cabal would also be appropriate.