if you are going for a powerbook you may like to think about a slightly smaller keyboard than the PCR50. they make another called the PCR-1A or something. Basically the PCR 50 is way too big to be portable which I guess is the point of the powerbook.
Also the PCR-1A is an audio interface. I think only a stereo in/out but I may be wrong.
As for the LaCie, I use a 160GB Lacie D2 on my 15" PB. It flies. It streams as many audio channels as I have needed it to without breaking a sweat. It's great for video work too.
Take a look around at some of the smaller midi keyboards at least. I believe M-Audio have one which is portable and contains an audio interface as well.