Benny Boy's good at speccing out builds, I've done a lot lately though so I know what I'm doing.

Before I spec you a build though I'm going to give my recommendations to you below.
1 - You have to look at benchmarks and look at price/performance ratios to make sure you're getting the best deal. Anandtech Bench is a good site to look on for this.
2 - Depends on experience and what kind of a system you're putting together. If it's your first time and you're building a system like your's, I'd say maybe an hour or so (not including installing Windows and software). Usually it takes me far longer than that because I'm a cable management freak and I like all my cables neat. I've got a PC I'm re-building at the moment and I started work on Monday or Tuesday and it's still not done.

But yes, usually a few hours.
3 - Get the best graphics card you can afford, then once you've spent the most you can on the graphics card get the best CPU you can afford.
4 - Depends entirely on what case you have, most have 2 or 3 (one intake and then either one or two exhaust). Higher-end cases usually have 4 or 5 fans (not including CPU cooler fan or power supply fan). I'd say a single fan is an absolute minimum, two preferably.
5 -
Case - Corsair, NZXT, Cooler Master, Antec (sometimes), Fractal Design, Lian-LI
Hard drive - Seagate, Samsung, Western Digital
SSD - Crucial, Corsair, SanDisk, Samsung, Intel, OCZ
PSU - Corsair, Seasonic, Silverstone, Antec, OCZ, PC Power & Cooling, XFX
CPU - Intel, AMD (they're the only two major competitors anyway)
Motherboard - Gigabyte, ASUS, ASRock, MSI, EVGA
Graphics (AMD) - Sapphire, HIS, XFX, ASUS, Gigabyte
Graphics (NVIDIA) - EVGA, ASUS, Gigabyte
RAM - G.Skill, Crucial, Corsair, Mushkin, Patriot
DV-RW - LG, Samsung
Cooling - Cooler Master, Arctic Cooling, Noctua
I'm sure there are others I've forgotten but you get the idea.
DVD burner - good
Processor - good (but the 3570K is newer but it's probably more expensive and the 2500K is still way more than enough)
Hard drive - get the Seagate, has twice the cache buffer
Motherboard - for 10 bucks more this is way better
http://www.newegg.com/Product/Product.aspx?Item=N82E16813128544
Video card - get the 6950 if you can but if you can't then a 6850 will be fine. There's always the 6870 which comes right in between the 6850 and the 6950
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102948
Power supply - good, if you get a 6950 you may want just a bit more headroom though, so try to get a 600W or 650W variant of that unit if you want a 6950, otherwise the 550W will be fine for a 6850 or a 6870
RAM - good (I think you linked to the same product twice though)
Case - this is better for not much more money
http://www.newegg.com/Product/Product.aspx?Item=N82E16811119233
Yes all would be compatible.