New machine specs?

Hi all,
I need to build a new acad computer to replace the aging P4 which means I have several questions:
1. how many cores/threads does the current acad
2. of the following, which is more important? cpu speed number of cores/threads amount of ram speed of video card speed of hard drive subsystem
3. Is there a big difference among scsi, ide or sata?
4. Does raid make sence for acad?
thanks for any feedback, charles.....
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