Write a business plan. You can find templates for them online it that helps. First, decide what you REALLY want out of this endeavor. If it's to quit your day job and spend all day at the barn, develop a dollar figure - how mcuh money will your boarding business need to make in order for that to happen?
I worked for a small boarding business where the owner's stated goal was for the barn to be big enough to pay for permanent part time help. The inconvenience of boarders and loss of privacy was worth it to her if she knew she had stalls, morning feed and turnout covered, and help with other work as needed. She didn't make money, but it was worth it to her if it meant she could have help with her own horses.
Do some local research about what board and services go for in your area, try to come up with a price point for your facility and see if you can make the numbers work.
You have two big advantages - the indoor ring, and that you do some training yourself. If you also offered lessons, that would be another plus.
The business model for a lot of boarding barns is to break even or even lose moeny on boarding, but to make it up on lessons, training and services. It's hard to make money on boarding itself because of the huge overhead, and that
There's usually someone up the road who's willing to undercut your price. Finding reasonably priced, reliable bulk sources for hay and bedding is critical, and if you're going to hire part time help, the quality of the help is critical. (You can lose a lot of money with an employee who pads their time, is heavy handed with the supplements, or can't tell the difference between the senior feed and the regular, and feeds the whole barn the senior feed.)