Yes, you'll have time to go through your stuff and pack it up before commissioning. I had my bags packed the night before and could have been gone 15 minutes after the ceremony ended (though I stuck around for a couple hours). You'll also be able to set up flights while you're at OCS--just hold off on doing that until it's pretty clear what date you'll graduate.
If you're not prior enlisted and don't have leave built up, you may end up going in the hole. Don't worry about it. Just be smart about taking leave afterward, and it will build back up faster than you think.