Good on you!! I volunteer at the local shelter and it's so rewarding. It's a whole lot of fun and you know you're making a difference. I've also found that working at the shelter has taught me soooo much about kitties, their personalities and how to deal with them, how to pick up signs of depression early on and picking up early signs of things like kitty colds. I thought I knew a lot about cats before, but this has really tuaght me so much more.
I don't have any cats at home (we've just moved to the US from Australia and had to rehome our baby), and we don't plan on keeping any cats permanently while we're here, so I don't have to worry so much.
But... one thing that's useful is to get a bunch of big aprons - one's that cover most of your clothes. That way you can wear that while you volunteer and get fur and drool all over that, and just wash your hands and take the apron off and you should be right to go home to your kitties.
The kitties at our shelter that go up for adoption have all had tests for diseases and been vaccinated, wormed and had a dose of Advantage for fleas, so generally they're fine in that sense. The only problems kitties have had who are up for adoption, is kitty cold and one had worms. Worms would be hard to bring home, and I'm not sure how a kitty cold is transferred, but I daresay hand washing and wearing the apron at the shelter would go a long way in preventing that.
Good luck and have fun