+1 to the gasket kit. They are cheap and you should replace them all. A kit comes with all 5 gaskets for about $5 and it takes you 5 minutes to change them out. Well worth it in my opinion. I bought a keg once that just reeked of sprite. Couldnt wash the scent out of the gaskets. With rootbeer, its even more noticeable. You dont want those flavors or smells in your beer.
As for the co2 tank, I'd start to check out craigs list. You're bound to find one there. Another good place to find a less expensive tank is a used restaurant supply store. The regulators can be found on craigs list too but Ive never really seen a good deal on a regulator. They all come in around the $70-$80 range.
Good luck, man. Once you start kegging, you'll never look back!