Few things since your asking
- RAM: 4GB is fine, 8GB is lots.
More ram makes the system slower, more banks of ram, more addressing to read/write, more time to do that.
- HD: Get an SSD for OS/Game, and a 7200RPM for data.
SSD best for performance, it would take alot of parallel drives to come close. Cost/power/noise would not be worth the return. You would have to be running a serious server to see the benefits I would think. Home user using apps SSD is perfect.
- Case: If overclocking, good air flow. Lots of choices really.
- CPU cooling: OC'ing = need for aftermarket.
Good air cooler is $40-$70ish, google can give you lots of test results.
Water, did that 2 computers ago. Silent and effective, hands down. That being said it's a little more parts/know how/maintenance (not a lot though, but still). If you want to do it, I would say go for it, kinda fun to tinker and works like a hot damn. If you want to put a case in a spot and forget it, go with high end air.
Side note with water, if you go that route, get a case that matches that well. Something like a Corsair Obsidian Series 650D, as an example for a case that I believe can have a rad mounted and has good fans (and a controller built in).
- Video: It's just me (a gamer) but a system this nice, you might find a better card for not a lot more, just a thought
I will PM you a site to check out as well, it should be a great resource considering all these questions you have asked