How many of the accessories are needed for 1 card? I currently have one 5970 and needs water cooling. How's the life of the gaskets? Still holding the water in?
Balanghai, this is what you need for 1 card.
1 water block for the card itself, and then the following loop:
Reservoir -> Pump -> Radiator -> Water Block ->
As you can see, it makes much more sense to do two instead of one since the only extra piece is one more water block. You can also buy a water block for your CPU later if you like.
I dont quite know about the gaskets. Some are in better condition than others. You will need to do a leak test for 1 day to ensure no leaking.
http://www.youtube.com/watch?v=Dk3V64ZSsEI