Nanshork, I heartily recommend using the Versatile Spellcaster trick for early entry into whatever PrC has the lowest casting requirements.
That, and Versatile Spellcaster rocks.
Early Entry < Feat Starvation.
Versatility > Intensity.
Wouldn't give me early entry anyway, both PrCs require 8 ranks in skills.
Hmmm, shame.
But I'm sure there's something else we can fit in there.
Trust me, five levels of sorcerer grates on me. If you come up with anything better let me know!
You could abuse taint mechanics (and your familiar) and enter rainbow servant at 2nd level. Necropolitan will get you a bonus feat, and the requisite taint level simultaneously. You'd have to shuffle around your feats a bit, though...
Four levels of RS gets you good and air domains, detect evil at will, and a fly speed for four minutes/day. The rebuking air creatures ability is probably the only relevant domain ability, but it's pretty nice to have a little cohort of green wyrmlings or will o' wisps. To fit with the theme, though, I'd recommend ice paraelementals or ice/snow weirds. The weirds are pretty much stationary, but they get awesome spellcasting.
EDIT: Ack, curse you second level necropolitan requirement! Some other undead is an option, though, since the undead classes in LM can apparently be multiclassed with freely (LM34), and the lich and ghost savage progressions can as well.