Espalier looks beautiful, but it's definitely not low-maintenance.

My suggestion is to make a map of your place, and cut out pieces of paper with circles cut in them to represent the diameter of the trees you'd like to plant. Consider the needs each each type of tree, the height they get, their relative beauty, etc..

The circle size is, of course, variable. It depends on a lot of factors. The most common mistake is spacing things too closely together, so make sure you give everything some room. One thing I've tried is taking a stake and a piece of string in the real location and moving it around to get an idea of how big the tree will get.

If you're the type that thinks this is fun, there are a lot of tricks to keeping things in a smaller space. If you take the grafting class, for example, and spend some time here, you can try some experimental ways of grafting dwarf pear trees (on apple rootstock!). You also can get a lot more varieties in the same space, because you can graft as many varieties as you want on the same tree. It's pretty easy to learn (the Home Orchard Society has cheap classes), and it's super fun. But I'm a plant geek.

If you want to economize on space, definitely get dwarfing rootstock. You'll have to stake it and water it. But it will take much less space.

Also consider things like grapes, which grow fine on fences or vertically, and take basically no ground space.

Feel free to post pictures and plan and what you're thinking. I think you'll find we're pretty eager to help.