Overclocking will not make a huge difference. Remember, you're just starting out - you won't be maxing out your processor or RAM any time soon. Also, overclocking is mainly for experienced computer builders, and should be avoided by novices as it's very easy to blow something up (or melt something).

I would recommend CentOS as your operating system, as many large studios use this as their base.

I also think that a 500 GB boot drive is excessive. Our production boot drives are at max 120 GB. This would hold the OS installation, as well as any of your applications. Everything else would go onto your larger drives.

I would also recommend using RAID-1 on your data drives. What this means is that one drive is an exact copy of the other. This way, if one of the drives fail, you have a complete backup without having to do any extra work. It also has some performance benefits as you now have two (or more) drives that can service the same request for data. This means that the arm of one drive doesn't have to move across the platter if another drive's arm is closer. There are other RAID levels, but it becomes a complicated subject. RAID-1 is pretty foolproof. Note: When RAID-1ing drives, make sure that they are the same model, otherwise performance will the be same as the slowest drive for both disks.