In order to stop people spamming roles with hundreds of suggestions, how about a limit of 5 suggestions per search (you can add more but you'd have to go back and reopen the search, not a problem for most users but slows down spammers) and an overall suggestions limit per 24 hours for each user.
Casting suggestions limit.
I'll have to disagree with you on this one, users want more suggestions if they want, and no limit's forcing them not to.