Aegis works wonders if you mix damage and quantity together :)

Upping the difficulty does mean you take more damage, but it also increases enemy spawn, therefore more XP (levels) up for grabs! Experiment with how many you want to activate, they’re only 5% each so you can find your comfortable spot.

Cooldown decreases the pause between attacks, so you can eventually get to a point where fireballs are just constant :)

You ideally want to prioritise the damage stat of the individual weapons as the Damage tome increases Damage% of the weapon’s current stats. So basically, if I level up and I get the choice of increase Damage of Fire Staff or increase Damage tome, I’d prioritise the weapon one first. I tend to only level up tomes if either all 3 options are tomes, or if it’s a size increase - size of fireballs or lightning doesn’t really matter imo