Agouti and capybara can work together - I've seen photos of zoos that have had them together. I almost tried that mix once myself, but was worried the agouti would be too vulnerable to predators in an open top exhibit, and too difficult to catch up each night.
From my experience, I would not do squirrel monkey or tamarin with small, flying birds - and by small, I mean comparable to them in body size. Ducks, curassows, screamers, sure. Anything else, not worth it. I've seen several wild passerines caught and killed (slowly) by squirrel monkeys. And I have a friend who once had to rescue an amazon from a cotton top tamarin that was literally riding it like a Pegasus as it flew around the enclosure, trying to dislodge it.