The barn where I board has a loft apartment and those that have boarded there have loved it. But there are stipulations:
1) Make sure there's an escape route outside of the barn.
2) Don't put it over the wash racks. Warm, moist air rises -- right through the floor!
3) Place plenty of plastic vapor barriers on the outside of the floor insulation. All joints should be thoroughly caulked.
4) Windows and doors should have heavy-duty weatherstripping.
5) Many horses are noisy sleepers and some are very active during the night!
6) Estimate the size you'll need, then double it!
7) Place all lighting and receptacles for the apartment on separate circuit breakers from the rest of the barn.
The inherent vice of Capitalism is the unequal sharing of blessings. The inherent virtue of Socialism is the equal sharing of miseries. Winston Churchill
I boarded at a barn with an apartment attached on the main level. The main access to the apartment was directly off the main aisle of the barn. I didn't particularly like it from a boarder standpoint, since I often felt like I was in the middle of their house. But that may have more to do with the attitude of the owners and less to do with the barn configuration. She would often comment that she could hear us in the indoor, since it backed directly up to her kitchen. She also frequently complained about her house being dirty, as they did not have a "mud" room off the barn entrance.
I would say privacy would be a concern any time you need to have others come in do do any work in the barn, more to consider if you have boarders and students coming and going.
As convenient as a dwelling in or attached to the barn seems, the 140' from my house to the barn don't seem really that far.
Our fire department reccommended a minimum of 100' and to keep easy access all around.
Some of those setups in links provided here are sure very nice looking.
I still think that the IDEA of living in a barn has much appeal in itself.
I'm so sorry to hear about your situation. You can check out our new facility, it's not done yet but we're hoping to be in by spring. My apartment is going to be above the viewing lounge in the indoor. It's 29 stalls, so it's a little larger then you are looking for but you may be able to get an idea by some of the pictures. You can look under www.cpequestriancenter.com and there are a few of the barn under construction in the photo gallery.