First, just to clarify. Has the OP actually focused the main camera yet? If not then that has to be done first. Then when you start trying to get the OAG in focus take long binned 2x images - I use 10 seconds and look closely at each shot as you move the guide camera in and out.
Second, trying to do long exposure imaging at 5.6 meters of focal length is going to be difficult and frankly a waste of time. At the image scale with any camera I can think of you're way over sampled to the point where you cannot get more detail than you would at 2.8 meters unless you can put the telescope in outer space.
Finally, trying long exposure imaging at F20 will require very long exposures (like 30 minutes or more) to get sufficiently above the read noise.
The barlow is pointless. I image at a Bortle 3 site with 1.5 arc second seeing on good nights. Scopes about about 10" don't show more detail. Aperture is always helpful if you can match the image scale to the seeing, but more aperture just over sampling gets you nothing.