What is the problem with your printer? I have a CR10s that I have used nonstop for about 8 years. I made the mistake of attempting to purchase spare components to repair it. I suddenly realized I’d spent enough money to buy a new one. Finally, I purchased a new Ender 3 Pro for $99 from Microcenter. I’m quite pleased with it.
It is designed to fit the stepper motor. My impression is that There is no reason why autofocus should not function.
I am not sure there is a well developed dark field option. I found this thread.