Recommend you don't post domain name suggestions publicly for obvious reasons. Maybe ask for folks to check availability then pm suggestions for available domains.

Regarding spam, would it take too much time to just verify new accounts manually? How many legitimate new accounts can you get daily? Just send a form letter email to all new accounts a couple times a day, personal responses with a legitimate reason for wanting to post get enabled, the others get discarded. The job might even be entertaining, and a nice way to meet new members of your community.

TT