a bit late but I read your post just now.
I'm living in Saxony, Germany. So I know quite a bit about the conditions you're working with.
We have locally the same problem with not only sandy soil but literally living on a really big sand dune with a bit of topsoil on top.
Read about or watch on youtube Permaculture strategies for deserts and drylands as that may be helpful unless you want to bring in a lot of clay to change you soil structure.
I do a lot of gardening and selling produce to the neighours and passersby and if I want to harvest a decent amount I have to water in july and august. So maybe some rainwater catchment might help to tide you over those months.
And mulch, mulch, mulch. Since I read about permaculture and started mulching every bit of soil that isn't completely overgrown, I have to water at least half as much as before.
Even if you can't fell the trees that produce so much shade, same laws here
many neighours just cut them down halfway when they get too high. So they are quite a bit shorter and need some years to regrow so big.
If you don't know if your soil is acidic try to google for "Zeigerpflanzen" there are some lists online. You only have to know what weeds are growing and they tell you what soil conditions they prefer and what you have.
We have lots of stinging nettle and it prefers slight acidic, nutrient rich soils for instance.
We have planted lupins in between the currants and mulch them with horse manure but this year I will try to establish some wood strawberries underneath maybe that works for you too.
I'm a bit more south than you so we can grow peaches but in our wet climate they are prone for fungal infections what helps here is to make "Schachtelhalmbruehe" (sorry don't know the english common name) and spray it over the trees.
Just try searching for the term "Pflanzenjauche" and you get a lot of recipes.