Yep, I'm having it built by someone else. I considered doing it myself but considering I haven't built a computer in so long I was a little worried of messing something up.
I hadn't really considered whether or not I would SLI at some point in the future. I had just figured the single GTX 480 would be more than enough on it's own for quite awhile.
Thank you for the PSU advice, definitely saved me some money from having to upgrade it unnecessarily.