New Computer

[Azathoth]

I'm thinking of getting a new computer.

I need to know:

a. If the below components are all compatible and should any be removed/replaced with something else.
b. How many hard drives a computer can have and if I could transfer the hard drive from my old PC and use it alongside any new ones. What is the difference between a hard drive and a data hard drive?
c. Where I can get computer parts assembled, and how much that would cost.
d. Whether or not I should by overclocked parts. What parts can be overclocked?
e. What is a PhysX card and should I buy it?
f. Should I get 8 GB RAM? Why is it possible to have 24 GB RAM, who would need that?
g. Wireless Network Cards are...?

Expert advice would be most appreciated.

Spoiler Alert, click show to read: 

Case: Will I need a really big tower for all this?

CPU: Intel Core i7-975 Extreme Edition

Cooling: Some kind of liquid cooling seems to be necessary for such a powerhouse?

Power: Thermaltake 1200 Watt

GPU: 2 GeForce GTX 285 2GB (Is there a benefit to having two graphics cards? What is the difference between the 2GB and the 1GB version? Between the 285 and 295 that justifies spending extra hundreds?)

Motherboard: Asus P6T Intel X58

RAM: 6 GB DDR 3

Hard Drives: My old one, 2TB Sata-II hard drive, ?Extreme Performance Raid-0 with 4 Identical Hard Drives: 2TB (500GBx4) SATA-II ?

Optical Drives: 16X DVDROM, LG 22X DVD±R/±RW + CD-R/RW Dual Layer Drive

OS: Windows 7 64-bit

Sound Card: Should I get any specific sound cards? I heard the Creative Labs sound cards have a lot of issues.

Mouse, Monitor, Keyboard: Eh, whatever.

Speakers: Should I get some?

Power Protection: ???

External USB Ports: Where would this be on the case exactly?