Which size drums on 69 Dart? And some other brake questions.

Yup- it SHOULD be 9 inch, but could have been ordered with HD brakes... you've got it apart, just measure the inside diameter. It won't be exactly 9 or 10 inches, but you'll be close enough to know.
There is only one hose going to the rear- the rest is all hard lines.
You could replace the cylinders without removing the shoes, but why? You should probably replace the shoes too, especially since the cylinders were leaking. Brake fluid does not play well with the friction material of the shoes...