Why don't you buy the last generation of Macbook Pro which was the best machine until yesterday and it will have all the features you want(matte screen, real button, firewire) and you'll save a ton of cash if you go refurb.
GIMP has supported editing all components of a path, converting to a selection, moving the entire path, and adjusting the handles, for a while. If I remember correctly, it was buggy until around GIMP 1.2.
The second half of the video on this page, after the "Direct Select" tool is chosen at 0:16, is completely doable in The GIMP.