I certainly read this with interest, as I would love to explore viable options of extra income from my small patch. I've tossed around the idea of growing heirloom vegetables, and selling seedlings. I've also considered breeding small animals and selling the offspring (although I do worry at the sort of homes they'd end up in, which can make letting-go difficult, lol).

Doing the research, finding a niche and quickly filling any gaps is a broad plan, but a sensible one (I hope). Feathers for crafters, etc is a good idea if the demand is high enough. Maybe check out places like Pinterest to see what people use (hence need supplies of)?

You've not mentioned small animals such as rabbits and guinea pigs - are these type of pets not something you want to get into? I ask because we do have the GPs and have had rabbits, although not for breeding to sell. If you had the time to shave them, Angora rabbits might be an option if there is still a market for their fur (knitters still use it, I'm sure).

When I was a horse-owner, there was always a shortage of good grazing, so this might be something you'd like to consider. You can (at least here) charge more for horse grazing than if you, say, rented the land to beef or sheep grazers; and in smaller lots.