For questions specifically about the Keil tools, you'd probably be best to go to the Keil site:
http://www.keil.com/discuss

If it's a presales enquiry, I'm sure their sales team would be glad to help you. Check their site, or maybe try
sales@keil.com

1) Networking is not a Compiler issue per se; you probably need to reverse the question: "what networking implementations have been ported to Keil"
In fact, any decent stack should be sufficiently portable to be compilable on any ANSI 'C' compiler.

2). This is standard ANSI 'C'
Keil is an ANSI 'C' compiler.

3). Again, this is not a compiler issue; it is up to you to deternine what goes where - the Keil tools provide full facilities to implement your decisions.
The uVision IDE includes a Code Browser; among other things, this can show you the most-frequently-used symbols.