The GTX660ti is not a particularly hot or power hungry card.
It needs a 450w psu with two pcie 6 pin connectors.
Buy only a quality brand like Seasonic, Antec, PC P&c, Corsair, XFX.
Here is a tiered by quality list to check:
http://www.eggxpert.com/forums/thread/323050.aspx
As to your other parts.
A pre built water cooler is an unfortunate choice for several reasons:
1. A i3 cpu does not need nor benefit from high end cooling.
2. all-in-one kits are expensive. A $30 tower type cooler with a 120mm fan will do the job.
3. water cooling will be noisy and less reliable.
4. When installed as per instructions, it will draw in cool air into the radiator to cool the cpu which does not need it.
The hot air is dumped inside the case which heats up the motherboard and graphics card.
My suggestion is to sell it if you have already bought it. The stock intel cooler will do the job but gets noisy under load.
If your use is for gaming, then a 2 x 4gb kit is all you need. No game uses more than 2-3gb by itself.
If you will be using 64 bit enabled apps, then 16gb(2 x 8gb) is good.
Ram is sold in kits for a reason.
Ram from the same vendor and part number can be made up of differing manufacturing components over time.
Some motherboards can be very sensitive to this.
That is why ram vendors will not support ram that is not bought in one kit.
Although, I think the problem has lessened with the newer Intel chipsets. Still,
it is safer to get what you need in one kit.
As to the case, if you have at least two 120mm intake fans, or the equivalent in output, then you will have plenty of cooling.
For inexpensive cases that meet that criteria, look at the Antec 100/200/300 series.