1000W PSU can handle it (especially Corsairs, I've seen tri-sli GTX 260's and GTX 280s so it should be fine). Water cooling? not necessary. If you can, add a nice side panel case fan, 2 back ones (120mm at least), at least 1 front one (120mm) and a top one (120mm). That should push a lot of air, keeping those cards cool, and allowing for some OC headroom. What mobo, be nice to know how much space you have.
I think the 1200 and haf932 are pretty close to each other in terms of cooling.With the HAF being $20 cheaper I'd say to go with it. I own an HAF and the 230mm fan on the side blows a good bit of air at my gpus. I would think tri sli would be fine in it.
That motherboard is not a good choice for tri sli. The third slot runs at x4.
This motherboards close to the same price and its third pcie slot is x8: http://www.newegg.ca/Product/Product.aspx?Item=N82E1681...
Having three gpus will cover all of the pci slots so if you need a wireless networking card you'll have to use a usb one.
If you're not Canadien (I don't know if you mentioned or not), try this. http://www.newegg.com/Product/Product.aspx?Item=N82E168...
It has *enough* of room between GPU's and has 16/16/8x SLI which is great. USB wireless networking card. Even if you did have space (you don't btw) it would just cause more heating issues.