For the mid, I plan to add a circular glass tube that people seem to get sucked up (trigger_push) to allow people to get from mid low to mid high. I'm also going to cut a hole on either side of the mid high to allow passage from mid high back to mid low, as well as letting the more experienced players jump from the mid supports into the mid high.
I'd brighten the dark lighting, but I don't know the key to change the value of a light entity's brightness.
Found out with a little Googling. The lighting will be significantly brightened.
As for the area right in front of the flag/spawn area, that might be a bit more difficult. What I might do is have a bit higher path (kind of like a large balcony) right next to the original path to the flag, and continue that path (balcony) into the spawn area, halfway around the room, adding a ladder up into the upper floor.