The mechanical resolution is the smallest increment of movement you require. For example if you have a mechanical resolution of 0.1mm you can never achieve a dimension of 10.12mm or 28.37mm. You could only get 10.1 or 10.2 and 28.30 or 28.40.
You need to make a decision on your maximum speed. A starting point would be to choose the maximum feed rate you will use and then double that for a rapid rate. Rapid rate is often overlooked when designing a machine but is important to consider if you want to have half decent cycle times.
Direct drive is OK for your application.
Measure the pitch on your screw. Its probably 5.08mm (0.2").
It doesn't matter if your other screw is a different pitch.
derekj308
<insert witty comment here>
derekj308