Nice case. I've got a friend who has an NZXT - prettiest little number I've seen. That one's even prettier... though, as one does, I prefer my case.

You might be able to get away with not having to buy any fans - the case comes with all seven already. The two rear exhausts, the top exhaust and front intake are what I'd advise, so those don't need changing, but you'll have to play around with the side four. If you go for a horizontal heat sink, then you should be able to fit all four in, but with a vertical heatsink you might not (if you do get a vertical heatsink, look for something below about 12cm high - my case is 25cm wide, and the heastsink sticks up 15.5cm from the motherboard with at most a couple of millimetres separating it from the wall of fans. The wall of fans are in the case though, rather than on the side panel, so you might have a bit more clearance).

With a horizontal heatsink, you'd want to suck air up through the heatsink, so the fan on that must blow up, and the side fan above that must be an exhaust. The side fan next to that (top right), above the RAM, would work well as an intake. The two above the graphics cards are the interesting ones - (1) if the graphics card fan sucks air in, then set the fan above it to an intake, and the one next to it (towards the back of the case as an exhaust). (2) If it blows air out, then swap it around:

[O][I] (1)
[O][I]

[O][I] (2)
[I][O]

Play around and see what works best. If things are still hot regardless of your configuration, then see if you can stick a 120mm fan in three spare drive bays and keep the door open, or buy some better fans.

As for thermal paste, you can choose from a number of types and makes. I use Arctic Silver V, simply because that's the one people recommended. It has tiny particles of silver in it which help conduct the heat from the CPU to the heatsink. Some people say that because of the silver it is abrasive and can wear out the heat spreader on top of the CPU (which begs the question - how on earth can it do that if the paste doesn't move as in, say, a normal computer?). As a result, these people use a ceramic based paste which does the job, but doesn't conduct heat as well as Silver V. Then there's MX-2 from Arctic Cooling, which is considered one of the best.

As with most things, personal preference comes into it.