planning our first forest garden!

Hi everyone! This is my first post on permies.com, although I've been avidly reading many forum entries over the last few months. My partner and I recently bought some land here in coastal Maine (zone 5), and we can finally realize our life-long dream of building a homestead. We have been reading and learning about permaculture and are particularly interested in food forests.

We have a south-facing area of about 1 acre that we would like to transform into a food forest. It already has 10-15 mature apple trees, about 20 ft tall. It doesn't look like they had been planted in any specific pattern, they're sort of interspersed in the 1-acre area, some very (or even too) close to each other, others as much as 100-150 ft apart. We would like to salvage at least a few of them, and also add some pear trees, and potentially plums, cherries, and peaches. I would love to have chestnuts and oak trees, too, and I know that we would have to carefully plan where to plant them given their height.

Now, my question is probably a very obvious one to most of you, but I can't seem to piece together the information I need from the books and online resources I've been reading - I have seen info both in favor and against of what we'd like to do. Are we supposed to plant our tall tree layer on the northern side of the area, or is it ok to have at least the smaller fruit trees scattered around (so kind of similar to how the apple trees were planted)? I understand that taller nut trees might have to be all the way to the back to avoid excessive shading, but I wonder if the area we have is large enough to allow for fruit trees to be spaced out and scattered around while still allowing enough sunlight to penetrate in the understory. We are also open to planting semi-dwarf varieties if it helps in this sense.  

I hope this makes sense - if not, I can try to sketch some examples of what we'd like to do and of what we've been reading about.

Thank you so much in advance!

EDIT - I should probably mention that there are two streams in the area, one on its western edge and one crossing it E-W (and eventually joining the other one).

I would assume that if you're planting them all at once that the trees will take care of themselves in finding what they need. And, depending on how you'd like to expand from there, I would definitely recommend a few oak trees because they're a keystone plant species. A lot of plants prefer to grow near them exclusively. But, all things considered, I assume you're buying seedlings/ saplings & transplanting them in, in which case, I don't think it matters that much.

With the streams you mention, I'm curious-- are they like little ditches that you can jump over, or wide enough that they disrupt the landscape a bit & would reasonably let in more sunlight into those spots?

Thank you! As for the streams, they are small. 1-2 ft wide. More of a ditch than a stream I guess :)