If you can afford it, the Gecko G540 can deliver at least double the performance of that drive. It's currently on sale for $210 (regular $299). It offers many features that the cheaper drives don't. Most important is mid band resonance compensation, which most of the cheaper drives suffer from.
If you go with the MDFLY board, about 5-6 amps is all you need. With the 1/2-10 screws, about 270 oz motors will give more speed than larger motors. HOwever, 1/2-10 acme will limit you're speed. A better choice is 1/2-8 2 start or 1/2-10 5 start, and 300+ oz motors. You'll get double the speed of the 1/2-10 single start.