Protools is hardware specific, you can't just get a copy and away you go, there is a version that'll run on some m-audio stuff tho, otherwise you're looking at digidesign hardware. TBH I'd ony recommend protools if you intend to invest serious cash in a protools hd system one day, otherwise Logic, Digital Performer etc are probably better cos they work with most hardware.
garage band is prety good for newb, and'll keep you entertained while you work out Audio Unit effects and instruments. Once you've got your head round GB, I'd recommend the new logic express (if you plan on staying with apple)- its cheaper than pro-tools, has a more modern interface and will lead on nicely from your gb experience.
Go for separate midi controller and audio interface (the macs behave better this way). You've plenty of 2in 2 out firewire audio interfaces to choose from too - which ted to have slightly better latency than the USB stuff.