Astrophotography can be wide field or narrow, like normal photography you need different focal lengths to frame different objects. Also like terrestrial photography, aperture is king. Planets need a long focal length and require video stacking to generate good resolutions. You are better off with a small ccd for planetary imaging than a dslr. For nebula, a scope or lens can be used. I have a 8" 1,624mm f8 Ritchie Chreitien and a 480mm f5.6 refractor. The rc frames m 101 pretty well, m51 is still kinda small, and f8 requires long exposures and good guiding. I'm going to go towards all wide field in the future. My refractor is very good quality but at f5.6 it is a tad slow. I want shorter exposures so I'm going for F4 or F 5. Honestly all of the old FD lenses, 500mm f4.5, 600mm f4, and 800mm f5.6 with Ed mika adapters would make superb telescopes. For me, I think 500mm is going to be as long as I'm going to go. I'm going to sell my cge and keep the zeq25. I will add a 300mm f4, a 135mm f2, and probably a 500mm f4.5. I'm considering selling my t2i and astro filters to get a 5dsr.
The mount you use is crucial, star adventurer is nice but will not take you far into serious imaging. If you want 300s+ subs then Get a good eq mount like the skywatcher azeq5, celestron Ava, or zeq25. Step up payload with an atlas or ieq45. Much more and you'll surpass your budget on mounts. Also, you need an autoguider package like the Orion ssag plus guide scope, and a way to mount the camera/lens/guide scope combo. Then you are gold. Image away.