1 - seeing as you will have to go ide -> adapter -> usb/firewire you're almost certain to lose some performance over the pre-builts that don't suffer from that obstable
2 - depends how well you vent your case.
3 - It will probably come with the adapater you'd have to buy to make it IDE2USB... USB/Firewire will not power it on its own.
4 - no help here
5 - Depends on what you plan on using it on. If it's Win2k/XP exclusive use NTFS. If you might use it on ME/98 as well Fat32
AMD Athlon 64 3000+ (Overclocked to 3300+)
1GB PC3200 DDR
2x200GB Seagate SATA RAID 0
BFG 6800GT OC w\\128MB Ram
2x 19\" Samsung 930B LCDs