Sent, if I can give another piece of advice, I would suggest doing things this way: Let us do Karmagen for creation (in karmagen rules, metatype costs are free), but lower the amount of karma for character generation according to the power level you want. This makes sense since all characters will be of the same "metatype", and it turns a bit easier for you to control to power scale.
I was toying with doing a 750 karma free spirit, and it turned out to be powerful, yet quite specialized and not uber-powerful.
I had written that, but you ninja'ed me. I will try doing a 400 BP free spirit. Give me an hour or so.