Edward - this should come out as a small system in HP SD terms, presumably you will use SQL Server for database and house it all on one box? There is in existance a spreadsheet sizing tool but nowadays disks are so large in relationship to the numbers it generates that there is little point! A 2GB database will keep you going for years!
Thanks Mike. I'm looking at the hardware question specifically. Disk is, as you mention, fairly cheap and generic. I was just checking that a single server middle range intel server would easily handle my proposed environment with decent performance.