The links provided are excellent resources. I highly recommend running a skimmer if you have the room, money, etc. It can be done without (I am skimmerless on my 20G), but having one offers an added level of consistency, ease of maintenance, and a little room for error, which are all very good to have on your first tank. As with most SW
equipment though, it's usually cheaper in the long run to buy right the first time instead of buying twice. If you get one make sure to research and buy right.