Spirit is your new aura currency starting at 0 and maxing at 100 base, with extra coming from special gear like sceptres and body armor. The whole aura system's different now since they don't touch your mana anymore, and you'll need to earn spirit by taking down bosses throughout the campaign

Managing curses got way more interesting, since marks don't count against your curse limit anymore letting you stack both at once. They've added a small delay when curses hit enemies though, and some classics like vulnerability work differently now reducing armor instead of boosting physical damage. Blasphemy support is still around if you want curses as auras, and there's even new stuff like hand of chayula for applying them

The big picture is you can't stack tons of auras like before, since spirit puts a hard cap on your permanent effects including auras and lasting minions. Its really about making smart choices with what you keep running all the time, especially since good Spirit gear will be pretty valuable for optimizing your build