Choice Of Multitrack Music Software Options

[keybie]

Reading the "rumor" websites to see if/when a new Powerbook is around the corner I'm ready to get one any time now. A 15" Powerbook that is, at 1.5 or 1.67GHz (or perhaps even faster?)

Anyway, I'm pretty clueless to the software issue regarding music making
So far (having used an Macs, pre OSX) I really haven't used Macs for music at all. What I have used (and still use) is an Atari Mega STe running Emagic/C-Lab Notator SL (the precursor to Logic on the Mac as well as on the Atari ST of course) as a MIDI sequencer, controlling my various MIDI keyboards, samplers and modules. Works great!

But I don't have anything to record audio with, which is where the new Powerbook will come in.For the time being I'm perfectly happy continuing to use the Atari ST for MIDI, and the MIDI modules as audio sources. But I would like to do multitrack recording, with some way to sync the Atari ST to the Mac (MIDI sync?) so I can add tracks. It would also be great if I could add effects etc. within the mix, and since my rack-sampler is time consuming and cumbersome to use (there's no hard drive for instance, so all samples have to be loaded from floppy disks) it would be very convenient with a "soft sampler" on the Mac which I could control via MIDI from an external keyboard just like with my external rack sampler.
I don't have any real need for soft-synths right now as I already have all the synths I need (and I like physical knobs and switches as opposed to using the mouse for everything), but this might be something to look into later.

So what kind of software will allow me to do this?
And what kind of software will allow me to do this and let me expand later if I want to go all (or more or less) virtual?

I've been told by others that "Garageband" which comes with any current Mac is something to look into, but I always thought it was more or less a "toy" where you cut/paste pre-made drum loops and all kinds of other pre-recorded instrument loops into "your own" songs. Probably fun to play with for a while, but not what I'd call "making music". But perhaps I've gotten it all wrong.
Does it do multitrack recording, sync to MIDI etc?

Then there's Logic express. I understand that it does "everything" -correct?

I really don't know what else there is.

As for audio hardware, I think I can do fine with the built-in stereo audio input of the Powerbook for a while as I have a decent mixer which is pretty flexible. Later on I might need more inputs, so expansion options for audio interfaces is probably something I'll need (or upgrade to a new program that does this if there is free software that I can start out with to begin with).

Thanks for any suggestions/comments