I'm not as knowledgeable as most here, but to give you a preliminary answer.

Keep doing Google searches for the Caapi. I've gotten it twice without going out of the US. Hell, I saw it on the big river although I would not recommend that.

It's legal in the US.

Caapi leaf is weaker than the vine. I did a 5X extraction of it and it works but you need many inhalations. I made a water and vodka extract of  Rue to make a "hash" which works on a few hits. Honestly, I generally mix up a bowl of the two and smoke that.

I almost always pre-dose harmalas instead of adding it to changa. I'm thinking you'd want to do an extraction for that.