[Wiz]

1. Custom Items, Monster Stats and spells. I've seen editors for these so I assume I can make custom items, mob stats and spells through those. Let me know if I'm mistaken.

Easily doable through database via the NPCs and Items tabs in EQadmin, or ItemEditor. Spells via Kayiodo's Spell Editor. Note that for it to work correctly you will need to distro your modified spells_en.txt to everyone who plays the server.

2. Change the experience needed for each class to level. So for instance if I want to make my classes level similar to the Experience levels of D&D is that possible?

Find GetEXPForLevel() in client.cpp and change it around. If you want to change the amount of exp given by a mob as it dies, find the ->AddEXP() in attack.cpp under NPC:eath. This requires a little coding knowledge, mostly ability to compile the source.

3. Change the amount of expereince a mob gives? Is it possible to alter the ammount of experience each mob gives when slain? Ex: I'd love to edit the Gnolls and have them mirror the D&D stats for hit points, Str, and Exp awarded. Can this be done?

See above.

4. Change the amount of Hit Points given to a player when the player advances a level? I'd like to make it similar to D&D. So a Human Fighter would get 1d8 Hps per level of exp, etc... Can this be modified in the server so that the Server Op can set the amount of HPs a race gets per level?

It's possible, but only serverside, which would create a rather weird mismatch (You'd have like 200 hp but the client thinks you have 1500) so I would not recommend it.