[Festin]

I recently used an O3L3 S9 Oracle as MA Ermor in Multiera Mithril Might, and I am very happy with this build. Got into lategame as one of 4 surviving nations an a major power, and only after a leading nation put up an Arcane Nexus I eventually gave up - even then my position was very solid and I could defend almost indefinetely, but AN is AN, so no chance of victory, and the micro was killing me. Overall, my most successful game so far.

Regarding the pretender: Ermor's mages are sacred, vestals are sacred, principes are actually hardly needed with all that undead chaff as troops, so upkeep is always low. O3L3 gave me a surprising amount of good events, and O3 is always good. During the entire game I was practically swimming in money, putting castles everywhere and spamming huge numbers of mages. I can't really remember if I was ever short in gold.
Also, Sloth 3 is an obvious choice. Free points, basically.
S9 is a great bless for vestals, so expansion will be a breeze.
Magic diversity is not that bad. You have as much D and S as you want, and a little A and W. Hidden in the Snow gives E and W, and then Hidden in the Sand gives F. Indies can always give you nature.