Alright, I'm fully upgrading my computer for like the first time in nigh on 6 years. I'm not really one of those conspicuous consumer-types that buys the latest thing every month, but I'm correspondingly inexperienced with upgrading at all, as a result. I'm aiming more "budget" here but hopefully not to the extent that it's completely (I'll settle for partially) outdated in a year. I don't mind running games on lower settings as long as they're playable. Currently my biggest gripe is that Planetside 2 is only getting 5-15fps in larger battles with my 3.1ghz Core 2 Duo.
GPU: For the moment I'm going to stick with my 285GTX until 6-series start dropping in price, I don't need DX11 anyway.
PSU: Sticking with my 650W, is that going to be enough for all this+ 3 hard disks?
Anyway this is just a rough framework and I'm more than willing to change it around at any suggestions. Only thing I ask is that I'd like to keep the cost pretty much around this. This will be the first "full" upgrade (Mobo and up) that I've handled completely by myself/without the help of IRL friends, so any first timer tips and do's/dont's? One concern I have is I'm not entirely sure my case can handle the motherboard, it's 19 inches long and 17 inches tall.
Another thing: I'm installing this on top of an existing operating system, what steps should I take to make it ready for the upgraded Mobo/CPU/RAM? Things I should uninstall first, etc?
Some/all of this may be incompatible or at least dumb so that's why I'm asking, I'm no pro at this.