I'm not real sure how to set up the crons, but the rule in the past has just been that as long as your not running your crons every minute, you should be fine. Even if you're running the crons like once an hour, that won't put too much stress on the server, just as long as it's not a big long complex script, it should be fine to run a few times a day. If you have any more questions about this, just ask.
Thanks,