hardware editing video imac configuration

If you ask me, you can't ask for a better price/performance color grading package than the Matrox MXO with a 23" or 30" ACD. This setup will work pretty well (for the money) with Color in FCS2, or any other Quicktime-based color correction application.

The best connection between an iMac and a modern plasma would be an DVI to HDMI cable or adapter. DVI and HDMI use identical video signaling. You'll have to make sure your output resolution on the iMac matches the optimal resolution of the plasma (or at least get as close as you possibly can). Also, keep in mind that it often won't be perfect because a lot of plasmas don't have adjustable overscan.

I'm kind of confused about your third question. The only VCRs I can recall that even have Firewire interfaces are D-VHS units.

As far as your editing setup is concerned, I would avoid daisy chaining Firewire devices as much as possible if one of these devices is going to be your scratch disk. Doing this will only make the scratch disk slower. As always, you can keep your project files on your main boot/applications disk (i.e. the iMac internal hard disk) but always keep your capture and render files on a separate external scratch disk, preferably connected via FW800.