1. being able to delete a post/topic should be a possibility
2. covered in 1.
3. yes.
4. no. that is just a pain in the brown peep hole. I joined the forums at nintendo and hated their promotion system that limits all kinds of stuff. It really breaks the warm and fuzzies of joining a forum site.
Also, I agree with benkenobi88, should edit posts. It would be better to delete them.
I am a developer and work a lot with databases, what does this site use? If you would like I could help out in my spare time, all I would need is exact requests of what you would like to be done / queried / created / etc.