As I said, Rack & pinion focusers work ok too. A crayford's not what I would call a mandatory item. BK7 is just a special kind of glass that the main mirror is made of Lacey.
I'd say just get the GS dob 'as is' from Andrews....But of course, that's just my opinion. If you wanna do any up-grading to it after you've got it, I'm sure we'll all be able to help you out with info on how to do that as well...
Good luck with whatever you decide to do.
