"Overall mana-regen is slowed compared to what it currently is"
This idea should work fine, as long as casters aren't pushed even further into the ridiculous fight pattern of 1) Cast a spell or 2 2) Run around like a headless chicken hopefully getting enough mana to use one more spell on the tanky Dreadknight chasing you 3) Die, or spam Consume and attempt to flee while your enemy is frozen.
Also on that note, the 'wait time' casters are forced to take between killing mobs is stupid, it just makes things stop flowing and get very boring very quick. I have to grind by fireball until I'm at 0 mana, then run backwards for 10-15 seconds then keep attacking.
The rest of the changes seem good, as long as it's implemented in such a way that it removes/reduces my fore-mentioned playstyle.