New build with RAID0 4to5 TB of fast drives

Not sure I would use raid 0 for multimedia. If you lose a drive, you'll lose everything. But that is your choice.
There are drives specifically for multimedia use, CPU magazine used these in a recent HTPC build:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Here is the article, its a nice build. Page 46:
http://www.computerpoweruser.com/Images/SmartComputing/...

They are affordable 2 Tb drives. You may wish to research NAS enclosures as part of a media file server. It may be possible to set up a raid 0 in an NAS that would have some redundancy for drive failure, but I have no experience with that.

For streaming video, your bottleneck is likely to be your wireless network so I would look at high speed routers and adapters to sink some money into.