Swim has got substantial experience extracting mhrb and kava-kava with IPA, but not caapi. If it works with ethanol there is no reason to think it would not with IPA. The only obvious difference seems to be that you would need to evaporate IPA completely whereas with ethanol you may leave small amount of it in your extraction.

Yes. That's about right. The exact amount varies from person to person. Even for the same person it varies substantially, depending on many factors.