The game is an online game that uses webservices, is this going to be a problem on OS3.x? I haven't done much research yet, but I suppose that even if I have to construct/parse my own get/post commands to the webserver, I should be able to implement this, correct? Anyone have first hand experience?
We've had to use several languages in our other ports of the game (C#, Objective-C, Java), I assume c/c++ is the only viable option for the classic Amiga?
If you only want to talk with HTTP to a server, there is no problem. Every TCP/IP stack on Amiga provides bsdsocket.library API, which is very similar to Unix sockets or WinSocks. Then you have to implement your HTTP client "by hand". About programming languages - yes, C or C++ is the way (except of some Amiga specific languages like E). C++ compilers may be outdated however, so C is safer.