First you need to decide on what type of barn you will have...western, english, recreational riding, etc. Your discipline will determine what kind of arena you will need, equipment you will need (cows, barrels, jumps, etc.) Are you going to be a "show barn." If so you need extensive grooming areas, and probably trailer parking. Second you need to look into insurance policies and zoning regulations for your area.
What I expected when I was boarding. CONSISTENCY, CONSISTENCY, CONSISTENCY. Nothing is worse than showing up at the barn and finding that your horses has been fed early or late and consequently ruined your plans for a ride. I am a very "hands on" owner so other than cleaning my stall and feeding on time...I don't expect anything else. In fact nothing angered me more than the barn owner taking liberties with my horse by deciding to change his schedule, see a farrier or vet without consent, etc.
Everywhere I've been there was pasture board and full-care board. Pasture board was $100-$200 a month and was just that pasture in a group with field shelters. Very hands off. Full care is usually stalled 12 hours, turnout in private paddock for 12 hours. That could cost $300-$500 around here.
My dream barn would NOT allow kids...sorry kids. It would be atleast 50 acres with an indoor and outdoor arena, plenty of trails, a 1 acre grass paddock for my horse to privately use during the day, and a stall attached to a run at night. Clean stalls twice a day. Feed twice a day. Barn owner on site 24/7 for security/safety. Open to me 24/7...I HATE the barns that say "closed on Fridays"...what the heck that horse is my property and I expect access to him at all times...sorry. OH AND A BATHROOM...that is SO IMPORTANT at a boarding barn.
Training is an entirely different barrel of pickles. For me to trust you you would have to have decades of experience in the discipline you were training, a successful show record, and reputable references of your training.