I would suggest you make the rue tea the day before, and let it decant overnight. That way, a lot of the grimness falls to the bottom. With rue, leave that grimness.
As to whether you can mix the two together, I would say yes. I had a similar question recently. The thread is here
https://www.dmt-nexus.me...amp;m=350328#post350328 However, as its your first time perhaps just do one or the other.
Some people have said that the two have different energies, that contradict. For this reason, best to try one first.
I would go for just the rue. Maybe start with 2g at first. Then, you can, if you feel, have more later. It is much less brewing time than caapi and will give you a good intro into the wonderful world of harmalas. Perhaps save teh caapi until you have enough to get a good feel for it. The time and effort involved with caapi makes it much easier to brew a big load at a time (ie. at least 250g).
Then if the first time fails, you always have more. You also have enough find your sweet spot without overdosing (you can build up slowly).
"Mama matrix most mysterious." James Joyce
"The next great step toward a planetary holism is the partial merging of the technologically transformed human world with the Archaic matrix of vegetable intelligence that is the Transcendent Other." Terence McKenna
Forgive, you'll live longer.