I only have experience with the first boxed set of Dark sun, and in there preservers are just like normal wizards, defilers get quicker advancement in return for their defiling. From the horrible novels it was sort of a choice at every casting, preserving seemed to take longer so increase spell casting times as a sorcerer and metamagic to preserve.
Your multisetting sounds interesting, beware of economics going into Athas, the metal an average character carries is liable to get them jumped as if they were wearing mithral.
Remeber that the races are pretty different culturally and physically there, halflings are deadly cannibals, dwarves are hairless, everybody has psionics, is high level and has super stats.
Jakandor, do you have the wizard, barbarian or combo module for the setting? If you have only one then focus on the one, Jakandor is actually better for low level because they have recovering magic knowledge and tons of low hit die zombies.