There is no gear that will reduce cooldown. You're stuck with waiting.
Summoning demons is useful, since they actually engage in fighting and can take the attention away from you. They act as tanks. Ghosts are semi useless because you shouldn't be needing a healer since you're away from the action, and there are other things you could better spend points on. Undead are absolutely useless, because you're the mage - why would you need another one?
Since you've already decided how to play your mage, what exactly do you expect from this thread?

By the way, I see you're still stuck on wanting to use fireball. That's great, since it's one of the classic mage spells from various games. The only problem is this: Fighters and Rangers can hammer away for tons of damage with swords and arrows in the time it takes you to wait for fireball to reload, making you very ineffective.
Fire
Wall expects the enemy to come in close.. If you want to let enemies close to you - you better have a lot of life and armor, or you'll be toast.
Fireball is a great opening spell, for damaging lots of foes at the same time, and okay for the occassional blast, but it's a very poor damage-per-second spell. It's not very effective in rapid combat. Magic Missile is the DPS spell for mages.
Explosive arrows, again, is what fireball should have been. It's more powerful than fireballs and you can fire them every 5 seconds. Bam!