Building a PC for raiding

[whathump]

I'd like to be able to raid 10 or 25 on medium/high settings on WoW, along with a number of addons, without getting low fps. I'd also like to be able to run Diablo 3 at decent settings.

http://pcpartpicker.com/p/Ccir

I just copied most of the 570 budget computer from Marest's thread (although I couldn't find the case on this site so I wasn't sure what case to use) and was wondering if this would be enough to do that with WoW. I'm also not sure what to do for a monitor. Just something cheap that will display everything fine and not take up too much space. My laptop has 1366x768 (or something like that) resolution, so something that's not too big of a jump would be ideal.

Also, if I already have a windows 7 disc with a key, but the key has been used on another computer, will I need to get a new OS?

I'm also looking for a cheap gaming mouse that has good number of thumb buttons (4+).

This is my first time looking into building all this stuff myself, so any help would be greatly appreciated.

[Butler to Baby Sloths]

1. Get two 4GB sticks, not 1 8GB stick. Much faster, and costs the same.
2. Case + monitor: budget? you can get a nice case that is easy to build in for 60-70 dollars, 1080p LCDs start at ~110 and go upwards.
3. If you use that Windows 7 key on the new PC, the Windows 7 on the old PC will be deactivated.

[whathump]

1. Get two 4GB sticks, not 1 8GB stick. Much faster, and costs the same.

Whoops, didn't see that I had selected the wrong one on accident.

2. Case + monitor: budget? you can get a nice case that is easy to build in for 60-70 dollars, 1080p LCDs start at ~110 and go upwards.

Well, probably about $200 to split between both. As long as nothing's overheating and the parts are protected (particularly from bugs that might try to get in, I live in an apartment complex that has pest issues), I don't care too much if the case is nice or not.

[Deleted]

@ Bugs: You're definitely going to want a case with air filters at the fans. I don't see how a bug wouldn't be able to access through the fairly large holes in the case, and the stationary fan(s) when the computer is turned off.

[whathump]

@ Bugs: You're definitely going to want a case with air filters at the fans. I don't see how a bug wouldn't be able to access through the fairly large holes in the case, and the stationary fan(s) when the computer is turned off.

I suppose the case would be fine if I kept it elevated and out of any corners or anything.