Good call on the macbook. I had 3 before switching back to PC, but that is because i play games and stuff.
I would focus your energy on Logic, and garage band.
I had logic pro for quite some time, and always ended up recording in Garage band. I loved the EQ and compressors.
Have fun, and take care of it. They last a long time if you take good enough care.
As far as the 4 gigs. That is perfect. I had 1 gig in my first two and it ran pretty dang good. And i was running a lot of VST's and AU's.
When i upgraded to the 2 GB of ram that shit flew and i had no idea what i was missing out on. Have fun and enjoy it!!!