After some thought on Mana, here's my new proposed system:
Each player starts with 300, and gains 100 Mana each day. Founts are as usual, but give 50 mana each. Destroying a fount still gives 100. Maximum mana is capped at 1000. Obviously the numbers might need to be adjusted. I think with this system it won't be as bad if you get unlucky, and there won't be stockpiling cause there's maximum mana.
I'm still thinking of ways to reward fighting over escaping in a way that won't harm Assassin and Rider, although such a feature doesn't seem that necessary to me now that I've had more time to think
Current situation on the classes: Assassinate is changed to 30d6 with Dastardly Finish banned, Berserker loses its extra feats but gains Mad Enhancement with a flat +6 to STR/CON and +3 to Will, Knight gains AC bonuses, nothing to the Rider (will leave Rider changes to future hosts).