If you've never grown fruit trees before then starting out small is the way to go. When I started I went with 4 apple and two pears. I learned about growing fruit by attending classes put on by the local university extension office. I've grafted a lot of my own trees from these classes. I have learned a lot from Tony Dembski at Maple Valley Orchards in Gillett WI put a lot of the classes on. Check your local county or university extn. I attached a link if you want to see if Tony has any trees left to sell this year. Here is a link that might be useful: apple trees

I think what you're dealing with are Pear Slugs, which may or may not be what Beeman mentioned above. I used to see them on my pear trees and would just squish 'em when I found them. I don't see them anymore. In small numbers they didn't seem to do much damage, just mining the leaf surfaces here and there. They are a serious pear pest though in other parts of the country. Here is a link that might be useful: Pear Slugs

The only one I can think of at the moment would be 'Lecont Hican', which is a hybrid between Pecan and Water Hickory (maybe it would get the wet soil tolerance of it's Water Hickory parent). From what I hear the nuts can still be quite bitter though, so I'm not sure if you would actualy want to eat them or not. Overcup Oak would be a great choice if you didn't need something with edible nuts. Here is a link that might be useful: Oikos

Looking good, congrats on the orchard. So did you plant your trees in compost? or was it a compost/soil mix? I have never seen anyone recommend planting in pure compost, and usually it is recommended that you mix in your native soil as well. Depending on your clay, you may wish to scratch up the sides of the holes as well, if the sides of the holes are smooth, you can essentially create a pot in the ground that the roots will circle and eventually choke the tree out (this depends on your soil and the rootstock of the trees, but just good practice to scratch up the sides of the hole). Sweet cherries seem to always be a challenge, i think i killed off 4 of them before i figured it out. Top of the hill is great to help with drainage, and make sure to mulch with compost every year (i recommend going 6-12" past the dripline). I would recommend moving the old mulch aside, adding in the compost, then topping it with the old mulch and some fresh wood chips every year (as needed). Apples will benefit from iron in the soil. If you have or can find some old iron nails, knocking those into the soil around the apple tree can be beneficial, or from amazon, you can buy iron shavings, mix that into compost, and apply around the tree as well. Spraying is never a one size fits all solution. for the first year, watch the trees, take notes of what you see, shouldn't be any reason to spray. next spring, before they break dormancy, you can hit them with a dormant oil (that Bonie horticultural oil can be applied at a higher concentration for this application, it should give you proper measurements on the label for dormant). Check with your local extension for known pests and diseases, then check that against what you bought. If the tree is resistant to anything that you have local, then don't spray (why fix a problem you don't have!). Neem oil is a good organic spray as well. if you end up with peach leaf curl, then you will need so treat your trees in the spring with copper. So really just watch for the first few years to see what your needs are.