Yes you gotta keep playing once you get the callouses. Because of an illness, I stopped playing for a month and found it very painful to play for any time when I returned to it. It didn't take much time to get them back again.

You also have to develop the muscles in your left hand and fingers. I think this would be the case with any acoustic guitar. You can get the action lowered until right before they buzz. If you plan to use open tuning, be sure to have the guitar tuned to the lowest tension you will come across in your choice of tunings. When you develop callouses and muscles, I suggest you get the action raised again.

By the way. A classical guitar can really sound dead if the action is low. This is not the case of most acoustics. They are just less loud.

Murray