You are an experienced programmer and have a problem with the engine, shaders, or advanced effects? Here you'll get answers. No questions about C++ programming or topics which are answered in the tutorials!
.map is a very popular format name - I've got about 5 different pieces of software on my pc which save to .map and all in different formats
BSPs could be used to design outdoor worlds - it really depends how big you want the world, how much detail you want and how the game works. You may find its better in the end to use a landscape class on its own and make a custom level format for placing objects on the landscape, or you could even combine BSP's with landscapes for some cool maps !