Hey Justin. Welcome to SWF.com! First you need to decide what you want to keep as far as fish and inverts and if you want to do a fish only setup (FO), Fish only with live rock (FOWLR) or a reef. Before you even set up your tank, you need to do a lot of research about each individual thing you plan to keep and its compatability with anything else that will be in the tank. A great starting point would be to read the Conscientious Marine Aquarist. Its packed full of information about how and why things are done in a marine aquarium, as well as tons of information on a lot of fish and inverts that are kept in a marine aquarium. That would be a good thing to do over your christmas break. For now, as I'm sure you'll take a few visits to your local fish store (LFS), please dont let them talk you into things they say you need, and always ask us here about the advice they have given you. LFS's are notorious for giving bad advice, or only half of the information you need to know about something, so you'll have to go back and spend more money. When I say research everything that has to do with your tank, it means everything. This means skimmers, wet dry, pumps, lights, sand, live rock, ext. This hobby is very demanding, expencive and requires a LOT OF PATIENCE!!! Lots of people average about $40 invested in their tank per gallon in even the simplest setups. 150 gallons is fine to start with as long as you do everything by the book. It simply means any mistakes you make will be much more costly than with a smaller setup. I dont mean to scare you, I just cant stress enough that this hobby requires a lot of research and patience. If you do your research properly, you should have tons and tons of questions. We'll do our best here to help answer them all for you. Best of luck Justin.
PS. Quarantine all your fish before you put them in your tank!!! Research that too!