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Astrophotography is a whole other rabbit hole to go down, although how deep you go depends on how hard core you want to get, what equipment you already own and the depth of your pockets. If you need a long lens for another aspect of photography, it'll open up a few more possibilities when shooting the sky. All I needed was a 2" prime focus adapter to use my a6000 with my scopes. I have considered something like the 200-600 zoom and a TC because that would be handy for birds too.

As mentioned above, sharpness will become even more critical when you are doing astrophotography because even a tiny error is easily noticeable with stars in the image. Focus is my biggest problem because it can look sharp in the viewfinder, but can end up revealing focus errors when viewed on a screen. Stars require perfect focus.

Seeing is another problem when you start using any kind of magnification and when your exposures start to get longer, and then there's blurring from the Earth's rotation. At first I thought my image of totality might have been blurred by thin passing clouds but there are two stars in the image that are tiny round disks which told me my focus had drifted. Still looked great in the viewfinder. If I hadn't been chasing sucker holes in the clouds, I would have used my Bahtinov mask to focus on a star first, then move to the moon, but I felt pressured for time so I winged it. Sometimes when I'm not sure of focus, and I have the time, I'll bracket my focus a little.

It's very common for people to think that the best time to look at, and photograph the moon is when it's full. Unless you want to get a shot showing the rays around the larger craters, its not a good time, because as Ivan said, the moon looks flat. Having some shadows reveal details and give a sense of depth.

Jim, what brand is your 6" reflector? I'm curious because f5.6 is unusual.