In Michigan I'm on the warm side of 4 and the cold side of 5 so I'm a slight bit warmer than you are. You can see in my blog what I am growing here. I have in the past had good crops of peaches, apples, cherries, plums, hazelnuts, grapes, and many others..but this past year (2012) we lost nearly all of our fruit to a hard late freeze. I'm hoping that doesn't happen again but it is something that happens in these zones. You gotta realize you will have some very bad years. In the past I have also had evergreens freeeze to death from cold winds, so windbreaks are very important in these climates.
I also have a small
greenhouse so that I can extend my seasons, but I mean small. I know if I had more coldframes and a larger
greenhouse I could do more..but I don't.
As far as the food forests, first and most important is establishing a windbreak or some type of protection for your food forest, and also making sure that the trees that you plan to plant are the hardiest ones available. Canada has some really great nurseries up there, so buy from those closest to you with similar conditions and they
should perform well for you. As for those pesky late freezes..good luck with that..I have heard in some places burning smudge pots works or spraying with
water (if you can find a hose that isn't frozen solid).