well first thing - throw the apple away, build a linux machine - virtually identical, about 1/4 the price, that got nothing to do with 3d printers - just general life advice :-)

Most 3d printers are pretty easy to service and repair.

The monoprice mini is a good place to start. Decent little machine.
Wouldn't worry about com ports - you'll most likely use the card reader and control panel to run most prints anyway.
If apple want to bugger up your computer with a new os - don't load it. It's your choice, not theirs :-)

Judging by your back ground the mini will be nothing but a launch pad into maybe a kit and then most likely just building your own from scratch. Actually a lot easier than you'd think.
But yep - good place to start.

And no matter where you get it from - you'll do all the servicing yourself, 'cos once you've got a 3d printer, you won't want it out o action for the length of time that sending it back to the manufacturers takes :-)