Hello,
1. If you don't mind the huge download, you will probably get more with the Microsoft tools: more optimizing compiler, more samples, more #include files, API help file, and an emulator. With Pelles C, you will probably get more of your requests implemented, within a shorter time-frame (at least if the requests are sensible).
2. Pelles C is for Windows (desktop), Pocket PC and Smartphones. LCC-Win32 is another compiler system based on the LCC compiler (by Hanson and Fraser). Only the *original* compiler is the same (more or less - we started from different versions), the rest is very different.
3. Never tried any GPS applications myself, so I can't help you there.
Pelle