What kind of apples are you growing? If they are a McIntosh or Jonathan type soft&tart apple, I would use a little bit of white wine vinegar, sea salt, and some lemon juice. Depending on whether you are going for a super-fruity or a savory background, you could either use an apple-pie spice blend (cloves, nutmeg, cinnamon, etc.) or more of a bite using tarragon, dill, etc.
In my own personal sphere of sauce-making, I have experimented quite a bit, and have found that minimalization of ingredients is best, so if you decide to use spices to accent the pepper/apple flavor, use care in selection, because some spices, even in small amounts, can drastically mute the pepper/fruit flavors of a sauce. Depending on your harvest volume, you could do small batches, and experiment with each one, and fine-tune the spices and other ingredients until you find a balance.
Too, it depends on whether you are going to eat it all to yourself, or whether you plan on sharing with friends/family, or selling it. If you really like spices, go all out until you find the perfect balance for you, but if you plan on giving it to other people/selling it, I would downsize the spice content to appeal to a greater variety of people.
Whatever you decide upon, good luck with the recipe! Sauce-making is a lot of fun, and is like a home chemistry lesson everytime you go at it!