I think this is a very good plan! There are actually two dental hygienists at the dentist I go to that own horses and work with horses a little on the side. I work an 8-4 job that is only vaguely horse related and I am able to visit the barn after work and over the weekend and work with my green horse and take lessons.
So many teenagers come online looking for ways to get started in the horse industry and don't have a plan B or plans for any other source of income. This is their first mistake. Horses are expensive and you don't become a reputable trainer, a well-known instructor, or have the finances to own or rent your own facility without some other way to support yourself while you work towards your goals. Kudos to you for thinking like an adult!