We have quite clay-ey soil, VERY dry in summer and pretty soggy in winter, we grow apples, pears and plums with great success, and if you're thinking of buying them, now would be quite good if they're container grown, but wait a month or so before planting so the soil isn't frozen. Bare roots could possibly go in now, but again, it depends on the state of your soil. You will have to cosset them a bit for the first couple of years, staking them, and making sure they don't dry out, and then, once they're established, they will probably need very little in the way of maintenance except for a light prune every now and then, grease bands in winter, and light mulching. Depending on your garden regime, and the pests you get locally, you might want/need to spray against moths and aphids at some point, but we don't any more, and we get good crops. The space each tree needs depends on the root stock. How much space do you have?
By the way, you talk about a single tree of each kind: have you thought about the question of pollinators?

It really depends on how much space you have.
The eventual size of each tree needs to be measured out then the double space before the next trunk calculated exactly before you plant the next one.
Clay soil is awful. I would dig a big hole and put a bag of good quality compost in, then plant the tree in it to give it a good start.
Maybe be best to just buy one the first year, to see how it prospers with your weather conditions.
Also remember to give a gallon of water every week for the first 2 years.
Patio trees are smaller.
Raspberry Canes do well in Limestone soil around here.

For apple trees, rootstocks are generally as follows:-
M27 - dwarf-bushes, really, and fans and cordons up to 8'
M26 - still dwarf, big bushes, espaliers or standards - 10'
MM106 Semi dwarf - up to 14'
MM111 - Big, vigorous trees, 16-25', need a big garden

The spread will be very roughly equal to the height, but is reasonably easily kept under control by careful pruning.
We have all ours on MM106, and they are perfect and easy to harvest. I think, as Diane has said, on a clay soil, preparation before planting is of paramount importance.
I have to admit that I know next to nothing about pears and plum trees, except that we have some, and they can grow really tall. I'm sure someone out there will know about relevant rootstocks for them, and a decent supplier should have the information you need.