You can get a free DAW for recording - Reaper, or if you want something more expensive, PM me.
All i'm saying is, if budget is a primary concern, then crezs USB interface will be all you need if used with your mixer and it's only £40. You could spend your change on another MIDI controller to help with your live performance. Otherwise, yeh the Fast Track is fine.
When you get an interface you'll be able to get a lead that goes direct from an output to the input on an A/B box. I bought phono to jack leads off Ebay. Wouldn't you want to run your bass and your mac sometimes though? If so you'll need some sort of mixer. One of the blender pedals might work better, putting the mac into the FX return.