At this point definitely go i7. There is no FSB because it's basically all asynchronous direct memory accesses -- they've replaced the frontside bus, essentially (oversimplification, but will do for the purpose of convincing Billy).
Asus P6T motherboard is perfectly adequate. Look up reviews. Let me know if you find any reviews that says, "is better than" in front of "Asus P6T".
Max out on memory. Make sure you get one that matches the capability of your CPU and motherboard, so that it isn't the bottleneck.
50 inch LCD monitor? You mean you're going to use a television as your monitor, right? Because the largest monitor I've seen is 30 inch.
1080p is easy, practically anything current (graphics-card -wise) will do 1080p. < US$100 Nvidia's constantly go on sale at NewEgg.
I'll let others answer the Raid question, as I haven't been following that at all. One thing I will say is someone mentioned to me that they wanted to Raid their OS disk not for safety/security/backup reasons, but to go faster. After they explained it (you're essentially hooking up the drives in parallel so that they act as one big multi-platter drive array that can deliver data amongst the "platters" simultaneously and independently at the same time), I could see how it might be a good idea in that particular scenario. I know this is not where you're coming from, but I thought I'd mention it if it interests you.
Fans -- don't skimp on cooling. Overclocking is one thing yes, but lots of video and music == lots of disk access, you want your hard drives not to burn up neither. Especially if you're Raidin'.