IMHO the mount is the most important piece of equipment, and I never hear people complain they bought too much mount. You have a good entry level mount picked out that is suitable for the first scope you envision. You might consider a larger mount if you want to be able to carry a larger scope in the future. Keep in mind weight ratings are almost useless for determining suitability for Astrophotography.
I would suggest rethinking the DSLR if you don't already have one. Most novice imagers quickly switch to cooled astro cameras and then you are faced with reselling what you are contemplating. A cooled astro camera is simply that much, better especially if the body is not astro modified.
I am more familiar with the Nikons so I will suggest a used D5300/D5600 and pair that with an old used Nikon 200 f/4 manual focus lens. I believe there are Canon equivalents but there are simply more used Nikkor lenses from that era on eBay. Alternate lenses would be any fixed focal length Nikkor lens with an F mount, which is pretty much all of them. An old AI/AIS would be what I would look for. Focal length of 135 f/2.8 or maybe even the highly regarded 180mm f/2.8. In my collection I have a 300mm f/4.5 that would also be perfect with the mount you are considering.
My quick search on eBay and a used D5600 goes for about $300, and a used Nikkor 200 f.4 for about 75. Keep in mind that any of these DSLRs will need to be modified to capture the light from Nebula in the wavelength of Hydrogen Alpa (Ha).
Zooms and autofocus is not needed. I would only consider them if you already have one or plan to use the camera for terrestrial work as well. This is even the case with the "pro" series f/2.8 Nikon or Canon zooms.