I have more than a dozen trees on M7 on a clay hilltop that is plenty cold and windy. Hit -27F here in January. They seem to be just fine. In a windy site I would stake for at least a couple of years.

I concur completely with marc although you may need to stake it for more than a couple years. My M7's tend to tip by about the 5th or 6th year and aren't a problem before they come into bearing. It may not be a problem with a crab at all. I wouldn't stake it for the first couple of years unless it is obviously needed, but would do so if it seems wobbly after that until it firms up as it likely will- eventually.

Stakes actually stop a tree from developing a good taper according to "the book" although apple growers use them all the time right from first planting and the trees turn out fine from what I've seen (and I've pruned thousands of such trees at various ages up to 40 years, at least)

Commercial growers drive the stake in the ground right against the tree at planting, so it becomes a pain to remove it years later- hate that. If you accidentally hit it with your saw it instantly dulls the blade and the tree will grow right into it, imbedding it into their tissue.

If you wait, you can actually drive a stake to tape to a single scaffold a couple of feet from the tree. It creates less rigid but adequate support in my experience.

Trees of Antiquity may have that variety on 111 although they may be sold out by now. M7 should work fine.

Thanks so much for the answers! I will go ahead with the M7 rootstock. I have been waiting to get a large tree removed and am so anxious to get this crabapple to try. Finally got the tree out yesterday so it's a go now :)