Board retirees. My neighbor had it great - about 3 boarders who never rode or used the facilities, and only showed up zero to twice a year to visit their horses. She stopped doing it this year because she thought she might sell the farm, but it brought in enough money to pay for her horses, too, and she didn’t have to deal with any of the issues most people have with boarders.
I wouldn’t do short term rentals unless I had somewhere to do them that was NOT in my house.
Giving lessons isn’t really my favorite thing to do, and if I had that sort of extra time I would probably offer dog sitting/walking instead
I know you’re somewhere on the Eastern Shore, have a fairly young child and are/were a teacher. How about tutoring or before/after school care for another kid?