Custom PC

I think I made a thread like this already, but my interest in building my own PC has popped up again. I really think it's time to upgrade my 6-year old dinosaur, and I'm trying to map out a plan in my head.

All I've thought of at the moment is to get a case first, because it doesn't make sense to buy a bunch of parts when I don't know the measurements. I will probably be getting a Smilodon:

Newegg.com - RAIDMAX SMILODON ATX-612WB Black SECC STEEL ATX Mid Tower Computer Case - Retail

Newegg has put a bunch of measurements for various sections of the case, but I'm not sure if it's safe to just buy standard parts like the motherboard and PSU based on that...does the case look like it will accept all standard-sized parts? Apparently, it's a very practical case, and comes with built-in fans and everything...but I just don't know.

Some other things I'm not sure about:

1. Determining what kind of PSU you need?

2. Mandatory motherboard features, and CPU compatibility?

3. Cabling that must be bought seperately?

The thing I really hate about all this is that I won't be getting all the parts at once.

Jam it back in, in the dark.

I don't plan to use the computer for any kind of gaming, but I would expect it to have very good video performance. I see that ATi is coming out with a Radeon HD 3800, which I'm assuming will be one of their best...if I were to pair it up with a Intel Core 2 Quad, would a 500 watt PSU cut it?

Also, pretty much everything connects to the motherboard, correct?

There's nowhere I can't reach.