Hi Ryan,

Let me just say from the start that the Heavy Mill 3DTEK as got some serious issues and it's far from its name suggests.

First off scrap the Z-axis altogether it's load of rubbish and far too flimsy. The Z-axis is THE most important part of the machine because it's where all the action happens. If it's weak then it doesn't matter if the rest of the machine is built like a tank your cutting will always suffer.
Also, no point using Hi-win profiled linear rails on other axis if going to use a round rail on Z-axis, use either all-round or all profiled. You are wasting your money mixing them.

Next is the Gantry sides, they are also weak and flimsy. They will resonate and flex which again transfers into the cut. To be honest the whole gantry is on the weak side and could easily be made stronger with a design change. Even the Light profile will work if you used an L shaped design.

Regards the ball-screws you will be better with 16mm x 10mm pitch for a wood router at this size. 10mm pitch will easily allow you to cut aluminum without any problems. Whereas 5mm would be too slow for cutting wood correctly.
You don't need 20mm for a machine this size and it will only rob you of power and speed because of the extra inertia of the ball-screw. It takes more power to accelerate and deaccelerate than 16mm and it does make a big difference to performance.

Regards the electrics and controller then always go with Ethernet if you can afford the extra, it's much more stable than USB or parallel port.

Andy mentions Voltage isn't so important but I'm afraid he's wrong, It's very important to the speed and torque you'll get from a stepper motor. The torque you get from a motor is proportional to voltage so if you increase the voltage the torque will also rise, up to a point. To get high speeds from a stepper you need voltage which is why we try to use higher voltage drives so we can boost voltage. Obviously there is a limit dependant on motor/drive specs etc but in general, more volts = higher rpm which is better for a router.

Regards the Motor, drives and PSU spec then there is a well-proven spec for machines this size which has been used for a long time on this forum. Which I'm happy to help you with. However, I'd also advise you to consider looking at Closed-loop steppers as they have come down in price quite a lot and are much better than the standard stepper systems. This could change things a little regards PSU etc depending on which you go for. So go have a look at them if you haven't already and let us know your thinking.?

BIGGEST ADVISE is don't buy anything else until your 100% sure it's correct. Also don't buy electrics until needed as your wasting warranty and things change fast these days regards controllers/software and drives you could end up with a better system by waiting until needed.

Don't be afraid to ask questions no matter how dumb you may think they sound.