Protools is a very strong piece of software... in some areas. I would not recomend jumping in and buying protools or an mbox off the bat. Digidesign has generally bad drivers. Protools also does not like to share the sound card so if you want to use another audio program with protools, it won't let you or you have to listen to the stuff with another soundcard. There is also Adobe Audition formerly Cool Edit. It is a very strong editing environment at a much lower cost and it will work with any professional sound card you choose. It it also plays nice with other audio programs.
I would not suggest that Adobe Audition is supior to Protools in everyway, but there are some other very strong programs out there besides protools. If you are really daring or want to do live music, Max/MSP/Jitter can do wonders. Protools is a versital program for very many things however, it is not for everything.
As for a macintosh, they are great but they have not improved their performance much over the past two years. I'd go with a PC since at this point, you'd get way more bang for the buck. Many of the people I know who do lots of audio are now thinking about switching to pc because of performance issuses.
For more portability, the Echo makes a set of high quality laptop cards and it can sample at 96kHz 24bit which is better than the mbox. It is also half the cost. It doesn't have a mic preamp though. But if you want quality input, you really want an external preamp. I can't really speak for the m-audio boxes.
Portable speakers are going to be hard to find. None of them are going to be studio quality. And even if you get something studio quality you are not going to have a proper room to put them in. And room sound is part of the sound.
Put out for some audiophile headphones like the sennheiser HD600s instead.
.... but to each his own. This is just my mobile studio. :)