Can I use props and textures from other valve games?
It is allowed, but you better don't do it. Try to stick with the tf2 theme and feeling.
As the amount of custom content in my and others maps grows I'm starting to get worried about uploading everything. With the source files my package will be huge, as will other peoples, and the tf2maps upload is slow (at least for me). The contest closes at the second mark, what if our stuff is still uploading? I'm sure most people will try and submit a day or two earlier but still.