Are you on a dedicated server? Then you're fine.

Most shared hosting plans are offering ridiculous amounts of bandwidth and disk space these days. What they don't tell you (explicitly) is that they have anywhere from 10-100 accounts per server, and if you don't play nicely with the CPU, you'll get kicked off. That is, if your host isn't dumb.

I doubt you're in any need of bandwidth or disk space with this site, so the first thing you should run into will be CPU usage. I suggest you never run captcha.