I mean, I agree there’s an attraction about everything coming from your own farm. If you decide to add “locally sourced” animals, just make sure you don’t use it as a crutch or shortcut to creating plant based dishes with depth. IME, if there are animal based dishes on a menu, it seems like the plant based ones become basic. Oh look, a curry lentil basil soup. 🙄 This is because we are so accustomed to centering animal meat in meals we’re not creative with plant based ones. Regardless of which avenue you choose (and it really feel like you made your decision about this business before you posted) I’d highly recommend you spend some time on YouTube looking up some great plant based chefs. You could pop over to r/veganrecipes for channel suggestions. You’ll be blown away by the myriad options that don’t sacrifice taste and complexity even though they’re not using animals in the dishes.
My other two points, which I think are probably more important, stand. I personally wouldn’t do this on an island unless there was a significant tourism industry there AND one in which you could pre-arrange relationships (cruises, hotels, resorts) that would guarantee traffic. Otherwise you’re going to be scrambling to find each individual customer and get them to walk through your doors. You need a relatively guaranteed source of revenue be it cruise excursions or government subsidies or grants from private foundations.
All the best to you
First, before spending anything, focus on that 83% of customers who aren’t coming more often. Who are they? How can you bring them in more often? How many of them would you need to come back, and how often, to turn things around? Existing customers should always be your first stop.
Next, I’d probably try to think of local businesses that have a similar customer base as your own and try to create a relationship. You have plants. What about relationships with landscapers? Decorators might need plants for hotels, office buildings etc. You have crafty things. Is there a fabric store in the area? A Michaels or Hobby Lobby? These types of businesses might have your same customer profile. Offering people who buy craft stuff at the local craft store a discount coupon to buy XYZ from your shop.
I’d do all this before I even spent a dime on marketing.