1. Don't know. Use polyworks, it's better then ANY soldat map maker.
2. They have to be saved files in BMP and PNG format, in soldat 1.5.0 gid support will be added however, the new version of polyworks is going to have to be released.
3. No, but you use lots on triangle polys to make other shapes.
4. Dont know what you're talking about.
5. I haven't really used map maker that much.
Use polyworks, it's WAY better. I'm serious.
Polyworks:
http://forums.soldat.pl/index.php?topic=174.0