Could you require that all new accounts require moderator approval before they are able to post?
I've been casually looking at the patterns of some of our bot spammers. they seems to coming through the captcha to apply for an account, but not actually posting yet. They sit there as "sleepers" for anywhere from an hour to a few days before they actually start spamming. I suspect they have a sweat shop somewhere where humans break captchas before passing the account off to the spambots.
If they choose a name that is a regex match to some of our most egregious spammers, /08*/, /lyjg*/, /sztin*/, we may be able to catch it and not confirm them. But in general, there is no way to Turing Test a new account to make sure they're not a spammer. We would probably be doing more harm than good, as people with "weird" usernames may be honestly asking for help but can't because we didn't approve of their choice of username.
Also is there some way to ban someone and delete all of their posts at once?
That would be awesome! But that would be a phpBB3 functionality, which I doubt they thought of that.