I cannot even begin to tell you what you are going to experience if you do open a boarding barn.
There is nothing but one hassle after another.
It is dirty, dangerous and all consuming.
The last big barn I ran was similar to your situation.
This young woman had taken lessons and liked horses.
Her father bought her a 30 stall barn with an indoor arena, outdoor arena, pastures and lovely house.
Because she had no clue, no one would put their horses in that beautiful facility.
She was in tears during our first meeting, afraid to handle the horses, (of the 8 horses that were there, 5 were hers).
They drew straws to see who would have to lead the horses to the pasture.
One horse got his eye kicked out. They almost got sued by their next door neighbor.
Even when I was BO, and the barn was full, we had a waiting list, it was a hassle.
People were never happy, my phone rang and rang.
Kids were climbing in my hay and swinging from my gates.
People would let the whole herd out trying to get their horse out.
And on, and on....you get the picture.
Lease the barn out to someone, that's what I would do if I was you.
Horses are proof that God love's us and wants us to be happy!