These are all valid questions. Csound for Android is relatively small in size. The OSX Csound package is quite large because it ships with universal binaries for both 32 and 64bit. One can create an entire Csound build on Windows in under 8Mbs. Keep in mind too that many of the plugin opcodes can be dropped when shipping. But I do understand the concern. For what it's worth Csound has only one dependency and that's libsndfile. If you only build Csound with this single dep then the footprint should be quite small. But as you add support for other things it does grow in size.
I have benchmarked Csound in VST plugins, and the performance is quite good. It has been mentioned on the Csound list that Csound code runs on average about 2-3 times slower than native C code. That's not at all bad for such a high level processing language. But it would take some implementation.
I would be most interested to see your findings. It would be great to provide this information for anyone thinking of using Csound in their games. Whats more, if we find CPU bottlenecks we can look at fixing them.