My barn is 36’x36’. If you were to bump out both sides of the roof line with full dormers, you would have a 1,296 sq ft to work with for living space. If 1/3 of the upstairs wasn’t a loft/storage area, we could easily have 3 bedrooms and 2 baths upstairs. The den, kitchen and dining spaces would be tight for 5 people, but it’s doable.
In a 20’x 24’ area we have a kitchenette (no oven), a dining table that seats 4, a large full bath, a 13’x12’ bedroom (king size bed), a 12’x12’ bedroom, and a den that has a sofa, loveseat and oversized chair. We didn’t put ANY closets in the space because we knew we only wanted short term visitors.
There is a hallway that leads to the loft space. From there you can access the feed room via a set of stairs. The stairs are not to code, but are FAR safer than a ladder. The treads are slightly narrow and the rise is slightly steep. We do have a VERY sturdy hand railing installed. I insisted on stairs and a second exit from the apartment in case of an emergency.
I have a toilet in my tack room so I don’t have to go upstairs just to use the facilities.
Make sure you REALLY research what’s required for an elevator. I have friends that had one installed (years ago) for a mother in law suite upstairs. It has been a nightmare of issues from the beginning.
The dumb waiter you mentioned sounds good as long as it can send up the groceries from the biggest shop you do in a month. You will have to go up to unload each amount the dumb waiter can hold. Also think about the weight it is able to lift. A case of waters or beer is heavy. It’s certainly better than having to carry it up the stairs, but it sure would be nice to be able to stack lots of groceries on top so you don’t have to make extra trips up and down the stairs.
One thing we added to the loft area was the ability to use an electric winch to hoist 300+ lb loads up to the loft. It required some reinforcement of the trusses, and it may never be used, BUT we would be kicking ourselves in the butt when we needed it Nd hadn’t planned for it.