On losing Manifester Levels: only one Psionic PrC in the XPH doesn't lose a Manifester Level at 1st (Elocator, who has ridiculous pre-reqs and loses at 2nd anyway), so you should probably do that. Losing at 6th also makes sense because Euphoric Might somewhat makes up for it, plus Euphoric Might is a much stronger feature than Avoidance (and Dependency is a bad thing, for the most part). So 1st and 6th.

I think losing more than that is a terrible idea.