Mid towers usually have room for 4 HDDs, but with the GTX 260's length you probably won't be able to use half of your internal HDD bays. Full tower gives you much more room.
The power supply I'm not quite sure on, 1KW does sound like overkill but I'd hesitate to go below 800W (700W Minimum) for SLI-ing those things.
A quick check of some reviews says that this psu
can power 2 GTX280s.
For the cooling side of things, there are a few things that can help.
The 260 spits the hot air out of your case...so that will help. It'l still be spitting it out into your room, but that really shouldn't affect your room temps that much.
To keep the cpu cool you should get an aftermarket hsf. For that, the freezer 7 pro
should do nicely (and don't forget the arctic silver 5)
You'll need fans to move air around inside your case, the general rule is match the in and out cfm. Good airflow keeps everything cool. Ignoring the psu and gpu, I'd have fans sucking air in from the front and exhausting from the back and top of the case. Speaking of the case, do you have one you are re-using or are you buying another?