My map compiles just fine, but when I try to look at a prefab in Radiant, such as a spawner barricade, it's completely invisible, the only way to select it is with pressing I, but I can't specifically deselect it.

Oh, gee, thanks...

When i go into a room that is completely, or mostly closed off from the outside, the brushes flicker as I move the player. How does one fix this?

Thanks in advance

Oh ok, yeah my methods works for the regular spawn mechanism, but there's no reason it wouldn't work for your version.

Can you define endless waves.

Yes.