Is it better to combine the b caapi brew with the mimosa brew after both have been fully reduced or to keep them separated? I have a concern that combining them will cause some of the mimosa to be metabolized before the b caapi takes full effect.

Ime/imo, it's best to keep them separate, some prefer to combine them, but it is more consistent and efficient to keep them separate, inhibit MAO-A first and then consume the DMT. There's no telling how many times i've seen people say Aya didn't work for them and they chalk it up to/blame it on something that it isn't, they forget something as simple as mechanism of action and dosage.