Have a look a Chillblast.
I would not bother with water cooling as it is more of a specialist area and does require more maintenance than the usual air cooling.
8GB is more than enough RAM for most of us and only if you were doing heavy photo editing tasks would 16Gb RAM be of benefit but then only marginally.
What you should be looking for is a decent Intel CPU, a smallish SSD (128GB) for your operating system and programs with one or even two 1TB HDD's for your games and everything else. I have a HDD just for my Steam folder which has around 400GB of games in it.And by keeping it on a separate HDd I do not need to reinstall all my games if I need to Reinstall Windows just do a repair of Steam and I am good to go.
Try and get a GTX 670 or AMD 7970 as a minimum graphics card.