Hi Alan,
At first I would NOT go for a laptop as a backup incase your keyboard fails.
For this purpose the MiniDisk is a very good/inexpensive option. It is small, easy to handle, selecting songs is fast.

For multi-track recording and sound-editing the PC or MAC is a good choice. As Chony wrote, the software depends on personal taste and requirements.

External soundcards :
Firewire types work great. M-Audio, Protools, Firebox.... etc.
(Try to avoid brands like Creative and Terratec)