I'm not at all an expert on the electrical components part and wiring of things. Usually I need help in this department, and I have just used a kit in the past, wired it as per the manual.
For some future projects, I would like to get into Arduino.
One thing worth mentioning is that many of the control softwares that people are choosing to use instead of mach 3/4 require you to use some of their proprietary hardware as well. So in essence you are using a hardware / software solution. I believe UCCNC is an example of this. Apologies if this was already mentioned. And correct me if I'm wrong.
Personally, I haven't found a commercially available control software that has anything too special to boast over another. I would like to see something that several different acceleration input parameters to take advantage of the increased torque from a stepper motor at lower speeds, instead of a single acceleration input into the software.
Some of the control softwares offer a separate input for rapids acceleration, which could be very handy, but still not what I would consider ideal.
For the typical DIY machines that we build it probably doesn't matter too much.
One thing I would like to know is what is the design of your machine? It looks like you have welded up a fantastic looking machine stand but are using T slot for the machine? If you don't want to work with steel, you can do some pretty cool things with aluminum plate. Is this still going to be a fixed gantry machine?
What are your expectations, what do you want to cut with it, and how well?
Two of the best DIY machines I've seen that cut aluminum super well are moving gantry.
It looks like you are using fairly large T slot extrusions, but I think you will have much better performance if you fill them with epoxy granite.
Also the quality of your build so far is very nice! Looks professional.
You asked about BST, I have ordered ballscrews from them, the review is in my thread here:
http://www.cnczone.com/forums/linear...-needed-3.html