The BitCurator recommended workstation (http://www.bitcurator.net/2013/08/02/building-a-digital-curation-workstation-with-bitcurator-update/)
is a good start. Barring any specific needs (e.g., you'll want to use Windows for migrating certain media formats, or OSX/*nix for heavy scripting/processing), most reasonable modern off-the-shelf systems should suffice.
The only real caveat is that you'll likely need more RAM than you expect - tools like OpenRefine and web crawlers can consume tremendous amounts of RAM, and virtual machines can use a fair bit as well.
Regarding media migration hardware, this should be dictated by your collection needs. If you don't have many floppy disks, you probably won't need fancy hardware; if you have a lot of CDs or Zip disks, allocate hardware accordingly.