A good first attempt! The KAF8300 sensor has shallow wells so it takes some effort to get good star colours (adding some short exposures with HDR is worth trying). Surprising how much Ha you got in 10 mins.
The big dust donut isn't going to be from your secondary. The dust will be much closer to the sensor than that. Here's a calculator that will help you determine where it is:
http://www.ccdware.com/resources/dust.cfm
Cheers,
Rick.