just to chip in - I use a celestron c11 with a feathertouch focuser from Starizona - backlash hasn't been a problem for me and I have used SGP since the early days. It has been difficult to get good focuser curves though and I haven't been able to work on improving it as the cloud cover at night has been very problematic here in the U.K. I can confirm though that autofocus works using sgp and the C11.
As has been advised, keep things simple to start, otherwise there are too many interacting variables and you can't pin down the problem.
Good luck with it - help here is first class as long as you can provide the information required for fault finding.
Paul