Just got into recording with my Macbook Pro and thought I'd buy Logic Express but decided to start with GarageBand and see how it went. It's been enough for me to this point.
I'd recommend starting off with GB and it may give you all you need for now. You can always buy Logic Express down the road.
does garageband work well with presonus and motu firewire interfaces? are projects from garageband able to be imported to logic or other programs?
You might hang tight until next week. Tuesday (1/15) is the next big Apple announcement at MacWorld San Francisco and you might be able to get your Macbook at a better price (or an upgrade for the the same price as you'd get today...)