Welcome,
In regards to fitting fruit trees into that space, and I've mentioned this before in several other postings mainly because it works, why not try to espalier fruit trees?
Google Image 'espalier' and you'll get the idea.
There's all sorts of designs that can maximise potential, and it will allow layering of both annuals and perennials.
Though, as others have said, that maple is likely to be a major impediment - any chance of it being considered a threat due to root disturbance (falling over in a storm) or otherwise mysteriously getting sick, prompting removal?