I don't think the size of the area for training doctors has changed much since VV4. I have never tried training 37 villagers at once in medicine, though, either in VV4 or VV5. Once they've reached trainee level, I'd try moving them out for a breather, and making room for training up a few more. When the game is off they will carry on learning , provided medicine is checked as their preferred skill. The space issue will of course not apply.