All of your cameras have pixels 3.75 um or smaller. That's really way too small for the HD1100 at f/7 for DSO imaging. I have the same scope at f/7 and use a QHY10 with 6.05 um pixels which yields 0.62 arcseconds per pixel. The central spot size is around 12 um with this set up, so the QHY10 has about optimal pixel scale for a fully sampled image if seeing conditions were ideal, which they never are, of course. So an even larger pixel scale would be reasonable. An alternative would be to bin 2x2 with your current cameras which would give a 2 times larger image scale and 4 time the full well capacity
One of the advantages of larger pixels is the larger full well capacity. This increases the potential dynamic range that can be captured in a single subframe and minimizes the saturation of bright stars which helps preserve star color in processing.
I highly recommend off-axis guiding at all focal lengths but especially at the longer focal lengths like 2000 mm.
I have not found the need for an additional focuser. I find that with a Bahtinov mask I can get very accurate focusing with the stock knob. Remember to always finish focusing by turning the knob counterclockwise so you are pushing the primary mirror up hill. I think more important is to combat the focus change with temperature that is magnified by the SCT design. This could be done with an external focuser, but I think attacking the fundamental cause makes more sense. I have replaced the aluminum optical tube with a carbon fiber replacement from Public Missiles. I have very little focus change now over a 20 degree F temperature change so I can go several hours without worrying about focus.
You mention cooling and that is more important with a carbon fiber tube, which has less thermal conductivity than the aluminum tube and will thus cool slower. I use the Starizona Cool Edge SCT Cooler to get the optics to ambient temperature at the start of the night. This draws large amounts of air through the secondary opening and cools both the primary and secondary pretty quickly. You may want to take a look at this review of both the Cool Edge and the Tempest fans that replace the rear vents:
I don't have the Tempest fans and have yet to do any planetary work, but I do not see any evidence of tube currents with the carbon fiber tube after initial cooling. This may be due to the lower thermal conductivity of the carbon fiber over aluminum which keeps the side wall cooling rate closer to that of the primary mirror. That's purely my speculation, though.