I am new to fruit also so I am going through this too. My understanding is the groups is just the time frame in which they bloom. A crabapple blooms for an extended period so they say they pollinate everything. Another good apple pollinator is Golden Delicious it is partiallly self pollinating. Some apple trees are triploids and require two other trees to pollinate. If you don't want a crabapple maybe try a 2 x 1 or 3 x 1 tree. So you can really mix it up.

Almost all apples and crab apples can pollinate each other, so as long as you have different kinds, I wouldn't worry about it. Crabapples are particularly good pollinators because they bloom for a long time. More importantly, what kinds are you planting exactly? When you say you've started some trees, do you mean from seed? Apple seedlings are very variable. They'll resemble their parents only as much as, say, we resemble our own parents. And if you don't know who the father (pollen parent) was, it's even harder to predict what the offspring will be like. What if that tasty light red apple of yours was pollinated by a tiny sour crabapple? If I were you, I'd make sure I knew exactly what I was planting, and buy some grafted trees. Then again, it can be fun to be surprised, so if you like surprises, enjoy.

Mark, I saw in this thread that 'myk1' recommended the tried and true 'Braeburn Apple' to you. While they do produce good fruit and may be tried and true in the region where he lives it won't work in central MN. Many have tried unsuccessfully to grow it here- in MN the tree isn't cold hardy enough, but the main issue will be ripening too late. It would surprise me if you ever taste a ripe apple from a MN grown Braeburn (if one lives long enough to bare). Sticking with the University of Minnesota apple varieties is the way to go. If the commonly found commercial apple varieties worked in MN the University wouldn't have started the breeding program 150 years ago in the first place. From (http://www.minnesotaharvest.net/apple_wealthy.htm) "The Wealthy Apple: Starting from Seed" In 1860, Horace Greeley told his audience, "Never move to Minnesota...you can't grow apples there!" This was the same Horace Greeley who was responsible for the grand command of the century, "Go West, Young Man!" For Minnesota, a pioneer land only two years into statehood, such a reputation was sure to be detrimental to efforts aimed at attracting westward-moving Easterners to settle here. His apple statement was true at the time. But even as Greeley spoke, a fruit-loving Minnesotan was planting and evaluating apple trees started with seeds collected from northern sources, even some from Siberia. As a MN fruit grower I would recommend that you get at least one Zestar tree. It is the offspring of State Fair, and shares its early September ripening date. Zestar is a large firm apple with a great sweet and tart flavor perfect for fresh eating or cooking. Other good UMN varieties include (honeygold, haralson, wealthy, macintosh, chestnut crab, regent, connel red...) With the number of varieties you have planted, you shouldn't have any trouble with pollination. If you do find that your early or late season bloomers aren't setting good crops flowering crab apples make the best pollinators. Crabs are best because they are selected for their extended bloom period and profusion of flowers (more flowers=more pollen). Make sure you choose an ornamental crab that sets fruit, the fruitless ones are sterile and won't produce viable pollen.

No you need another variety. But anything nearby even a crab apple will work.