I also should share some advice, since I have lot's of lessons learned from adapting gen4 electronics to nearly any system. I personally think your lead screw is a bad idea. Between backlash, friction, and just the slow pitch itself (z axis stock runs true 8mm pitch) so your 2mm pitch is going to be 1/4th as fast at best. Those big NEMAs will be screeming to make the RPMS and had better be low inductance ones with good stepper drivers and likely strong 36 or higher volt power supplies, just to make stock speeds in the 30-40mm/s feedrates. Further, big mistake that a bigger machine is better, especially true with ABS. In other words, if you have visions of building large objects in ABS-best of luck. The thermal contraction alone will either cause inter-layer cracking or just warp large parts. PLA is much better, but there are limits there too. So the problem isn't just the mechanics of the machine, but rather, the very material you are attempting to print with. And since you cannot print fast, a large print of any size on your machine might take 5-20 hours depending on how big or tall you go. There is nothing that can prepare you for a print that fails due to thermal stress issues after 10 or more hours of printing. The thought that you just wasted 10 hours, plus the high price of plastic these days, then the thought of adjusting a setting or something and waiting 10 more hours will definitely put you in a good mood. Even the idea of heated chambers does not solve the problem. All you do is build stress into the part, fine if you keep it at 100c for life, but as soon as it comes out of the chamber and hits room temp, the sound of internal cracks forming can be heard from 2 rooms away. It's a sound that brings your blood to a boil.
Please don't take this as a knock, just some tips from someone who has played your exeriment game and realized, the area of the cupcake was just about right. It's a shame but I own many, many printers, all of them custom, but the cupcake is the one machine, i can print something and know it will come out perfect. Anything bigger and the confidence level goes way down.
As cool as this one below is, It doesn't get the usage that the cupcake and real original Ultimaker printing PLA gets. http://www.thingiverse.com/thing:10380
Reprap
http://www.thingiverse.com/thing:8957
Tom in plexi:
http://www.thingiverse.com/thing:7063
(And sorry, the guy who cut that for me never gave me the tall files)
This bot gets the most usage and that's because it's PLA only, no nead for heated build surface, (painters tape on glass), accelerated firmware (yet another "must" you don't have and could be the deal breaker on those NEMA 34s)
http://www.thingiverse.com/thing:10802
It looks good, prints fast, is quiet due to the acceleration firmware and general design, and PLA hardly ever warps.
