Don't carve! I have to go to work RIGHT NOW but someone please help him to not carve. I can see the carving! ACK!!
You should func_detail those arches and stairs for optimization purposes. Select the brushes and hit ctrl+t. Read more on that here: http://www.optimization.interlopers.net/index.php?chapter=func_detail
In fact, I would recommend reading all of that. It is very important your map runs well.
Also. It seems very small, and enemies can see each other out of spawn. Reminds me more of a trade map than a competitive map.
I carved the steps in my stairs as well. http://i.imgur.com/P7pfX.png Does that look fine? Also how do I get those wall textures to line up? xD