If you were going to do a toss and wash with strong caapi, I would say a teaspoon, or maybe less.  Just enough so that you don't actually feel much of anything.

Also, SWIMfriend, there HAVE been literature that studies that CHRONIC use and RITUAL use of ayahausca.  It has been found to be VERY safe.  The Brazilian government did extensive studies on ayahuasca including "chronic" use.  I unfortunately don't have these on hand, but I can assure you they are out there.

Also all the ancetendtal evidence from curranderos that use ayahuasca daily/weekly since adolescence shows that it is not physically harmful as many live into their 80s and 90s with no western medicine at their disposal.