You won’t need the Io – but you could use it as a SD converter box (SDI to composite, s-video, etc…)
The Kona card will work just fine. Plus it also does SD.
You could use FW drives for DVCPRO-HD or HDV. The throughput isn’t very high. Only when you get into uncompressed HD do you need mad speed.
Go with at least 2.5 gigs of RAM, but 4 would be great (FCP maxes at 2.5, and that’ll give you extra RAM for swapping applications).
The Nvidia card is totally fine.