Yeah, there is more you should know - a whole lot more. Watch for our video course, "Wedding Video Done Right", info will be posted on
http://www.WeddingVideoDoneRight.com The first DVD of the eight DVD set, will cover, among other things what equipment you'll need, how to decide where to buy, etc.
As for your computer and software question, the current (and this changes about every six months) minimum recommendation I would give for a new system (one that you expect to be able to use without further upgrade for two years) would be:
* 2.4ghz dual core cpu
* motherboard with at least three pci slots & two epci plus two ide (to support 4 burners), accept up to 4 gb of ram and 3.0 SATA support with 4 or more SATA connectors.
* 2 gigs of fast RAM
* a video card recommended by your NLE with 256k or more memory that allows 2 monitors.
* system/program drive 160 gigs or more
* video files drive 300 - 500 gigs or more
* video temp files drive + spare storage 300+ gigs
* 500 watt power supply or greater
* two widescreen LCD monitors 19" or greater
* system case should allow 4 burners and have front connections for USB, Firewire, and other inputs.
All above harddrives should be 3.0 SATA and all the same brand.
Software - either Vegas or Adobe. My choice is the Adobe suite, about $1700 for everything, including Encore for DVD menu creation, etc. You'll also want Nero for copying DVDs (although your assumption that the average wedding client will want many copies is off-base).