No problem! If you want to do that, you use a thing known as a 3D Skybox rather than your own texture. It's pretty straight forward making one, you can follow this guide here: http://forums.tf2maps.net/showthread.php?t=116
Indeed you can! It's just a small area created outside your main playable area that's 1/16th the size of it, and it appears enlarged from inside the playable skybox.