The 1.5 KW is 2 horse power so that's still quite a bit of power. The 85byg450a is a good motor. I don't know the drivers, but it looks like it outputs enough amps for your motors.
I think you'll like your rack and pinion. I think it will have less drag than the ballscrew. And your linear rails and bearings are probably going to be better than my round rails and bearings.
I can't speak for all of their machines. I have mine and it is a great little machine. I helped another guy who bought a 6090A who lives 35 miles from me. He ordered his set up for Mach3. I was able to get it set up online through Crossloop.
I think in China, all of the factories copy each others machines. I think they don't have copyrights.
I think most of your Mach 3 code will probably work with NC Studio but I can't say for sure. I wish you'd have gotten it set up for Mach.
I did away with the NC Studio stuff and put on WinCNC.
As far as my picture goes, I gave a couple to Mandy. She was very helpful to me and provided me a very good machine at a very reasonable price. I figure that is the least I could do for her.
Good luck with yours,
Butterknife