The herp community will discourage mixing species, for good reason: it's very difficult to best meet the demands of a variety of species well. The few folks on here who are doing it well usually have large setups with similarly large budgets. That said, if your faux tree has branches down into the water so that a frog could crawl out then I think you can mix tree frogs and fish. I don't recommend a chameleon, the high humidity that the frogs require is likely to cause it respiratory issues.
If you haven't spent time on Dendroboard yet, time to head over--their Parts & Construction section of the forum is very useful for first-time viv builders. Most of the viv/pal/riparium folks on here can be found over there as well, plus a wealth of herp-specific knowledge.