Do some finances. There are plently of books out there on dealing with your student income (loan) and how to break it down over the term in a manageable way. Ask your Parents if they plan to support you in any way whilst you're at University. Mine don't, so I earn extra on the side to pay for extra living costs (such as food) and I put aside around £75 or so a month so I can play. Since I rarely drink (only when there's a hot girl), expenses are easier for me. I'm also in third year, and from my experience it is much easier to have a defined idea of how much time yu want to commit.
It's by no means a bad idea to play paintball whilst at Uni. You'll meet a great many people who have more going on in their lives than partying with the occasional lecture. It's also a great stress relief. But if you want to commit to a team, set an amount to the side every week/month and discipline yourself not to touch it except for paintball. This way, you earn a reputation as a player who can always be there. That, in my experience, is far, far better than a player who can play awesomely but only let's you know if he's coming the night before. As a society "official", that is annoying to organize.
Also, a couple of final notes, if you'd like any help when it comes to planning monies over the next few years, drop me a line and I'll be happy to help. There's also a Mercenary contingent of players from Uni's that don't have teams.