On number 2) and 3) I have the same problem. I decided to move an entire layer to another game level and it did help.
Other tips that might help you:
1)cut down on dynamics
2)make corridors narrow
3)too many entities will eat TONS of CPU cycles
4)distribute your NPC enemies evenly across the level. Bunching them in one area might slow your system down.
It does get horribly laggy compared to Source, Radiant or UnrealEd. I'm sure improvements are being made. I think FPSC is a good product. Will go a long way to becoming a fantastic engine. I love the user-friendly GUI, etc. etc.
Uh huh...thank you very much..