As noted by @blacksmith37, apricot and peaches are not appropriate to your climate. While they may live for a year or two, you will get a severe cold snap at some point that'll kill them at least down to the roots.
An aside - I once lived in a very similar zone 4/5 situation (we were hillier than your own situation, but similar soil and sun). The first year I planted a Contender peach - it died over the winter. The second year I planted a different "hardier" variety of peach and it, too, died, but only above the graft. The rooted section produced RED foliage that stayed colorful all summer. I moved it that fall. Every winter the foliage died back to the ground and the lovely new growth sprouted every spring, usually to a height of 6 feet or more. It was really a pretty accent to the garden. But - never a bloom, so no peaches (which I assume would've been lousy anyway, since they would've been produced by the rootstock).
So, back to more relevant information...
Peaches and apricots - don't waste your money. They will die.
Bartlett Pears are not reliably hardy above zone 5b, so you'll definitely lose them if you plant them. There are hardier varieties out there, but be careful! In my zone 4/5 sojourn I planted two "hardy!" varieties whose names I don't remember that grew well for seven years - and never once flowered. Most likely, the trees were hardy but the buds weren't and froze every winter.
Fuji Apples are, if I remember correctly, somewhat fussy (they like the Northwest US and are not, for example, grown much if at all in Minnesota or Wisconsin (zones 3-5)). There are a ton of other varieties to choose from, however - Honeycrisp, Courtland, Liberty, Macoun... the list is quite long, so you'll have plenty of options.
Yellow Delicious apples are definitely appropriate for your site., but make sure you purchase them from a Northern grower, not from places that have supplying nurseries in Georgia, Ohio, or Oregon.
Methley Plum is rated as zone 5, and is not to my knowledge grown in the upper Midwest due to hardiness. There are other options, both purple and yellow (most probably arising from Prunus americana, which is extremely hardy and makes truly fantastic jam).
I strongly recommend that you research fruit trees hardy in zone 4 and, preferably, zone 3, while avoiding any trees native only to zone 5 and higher. This should leave you with: sour (cooking) cherries, some plums, lots of apples, some pears, and mulberries.
To help you with this research, I highly recommend The Wisconsin Garden Guide, 4th Edition by Jerry Minnich (ISBN 9781934553329). This reference contains variety recommendations for mostly zones 3 and 4 for vegetables, fruit trees, fruit-bearing shrubs, and ornamentals. The sections discuss soils, climate, etc. It also discusses organic pest control. I believe that the most recent edition was published by Trails Books in 2010, so the variety information may be a little dated, but I think you would still find the varietal information helpful; it could also be useful as a springboard for additional research. This book has been in print for at least 35 years, so I'm not alone in my review.
As for the number of varieties to grow... How much time do you want to spend pruning apple trees into the correct shape, for example? How much time mowing under the trees to prevent competition/weeds? How much time installing/maintaining controls such as sticky traps? Are you able to protect the trees from deer browse? Antler rubbing? You're correct, I think, that getting the trees into the ground ASAP is a good idea in terms of actually seeing a harvest sometime soon, but I recommend that you consider the amount of time required for maintenance into your calculations because fruit trees are the exact opposite of a "low maintenance" garden.