Need to be more specific with the number of campaign level options. Is magic a thing? Tech level? Legal books?
I put a guide for d20 Modern spells in the handbook submission section. A few tricks for casting/psionic classes are mentioned in it. The big one is exploiting Minions (d20 past) for reducing the difficulty of incantations, though that's a bit beyond your level. In general, you don't want more than three levels in a base class because only a handful of talents aren't horrible. Despite their nerfs (covered in the guide) casters, manifestors, and pseudo casters are at the top of the pack, with some combat brutes (shadow slayer), Mutationist and Field Officer under them.