1. The lighting: You really mustn't ever submit a map without lighting. All it takes is a few minutes to scatter some basic point light entities around the map. It makes the map look exponentially better and prevents wierd optical illusions when you have a lot of grid textures on every surface.
2. The stairs: They aren't clipped. Use the tools/playerclip texture to make an invisible slope over the stairs, so it's like walking up a ramp rather than having your camera shake up and down. You will notice virtually every map does this for all stairs.
3. The layout: I know you don't have a lot of experience, so this is to be expected. Your map is FULL of incredibly long, straight hallways with little to nothing that blocks vision. What this means is that your map will be dominated by snipers taking shots at each other from the opposite ends, and anyone playing any other class will be at a huge disadvantage. This isn't Counter Strike, everyone doesn't have a rifle. The central death pit is way too large and easy to fall into, and the point is only accessible through a hallway that will be dominated by snipers and a completely exposed bridge across said death pit.
It's my opinion that you should scrap this and make a new map, preferably one with a more complex layout. Try sketching it out on paper beforehand and drawing in sightlines with a different colored pencil if you're having trouble conceptualizing.
Good luck!
