I wouldn't worry about pruning them, unless you decide you want to "shovel-prune" a couple of them. ;) I truly love Silver maples, and they are an excellent wildlife tree, but not the greatest landscape tree. There is a large 50+ year old Acer saccharinum about 25 feet from the southwest corner of my house. It provides important shade during the hot summer months, but that tree is a pain in the you-know-where. It has big gnarly surface roots that invade the lawn, septic tank, and have heaved the front sidewalk. They are very water-thirsty and I have had to slowly convert one of the front gardens to a xeric garden because the maple roots grow INTO the roots of the perennials, hogging the water. It drops about a million samaras in the Spring. They clog the gutter on that end of the house, which means I have to clean the gutters twice a year (if I don't then that downspout is clogged solid and little silver maples sprout in the gutter, lol). Oh, they also drop big branches from time to time. A good place for them to grow is a naturalized low-lying area, on the wet side, FAR away from house/gardens/septic system.

If the new situation is sufficiently different the leftover trees may just die instead. Where strong winds occur blowing over may be likely long before the tree has a chance to die in a drought or from sunburn. But it varies, each situation having its own combination of factors at work.

Silver maples have a very strong tendency not to grow with a central leader. A typical silver maple will divide fairly low down into 3 to 5 large ascending branches. Occasionally silver maples will grow one trunk up to 15 feet or more, but this is not typical. I have never done it with a silver maple, but you could try to prune the tree to grow with one main trunk up to 10 or 15 feet without too much trouble. If the strongest trunk/ascending branch is leaning a bit, it may not be a big problem. If you prune off the others, the one you leave will straighten up somewhat. It will probably want to divide into large ascending branches again, and you can prune it again to maintain the central trunk. But, personally, I would let the tree grow as it wishes, unless one or two of the lower branches are growing outward at angles that would make them a nuisance later. A silver maple with the typical form of dividing into large ascending branches fairly close to the ground (4 to 7 feet)can be quite attractive. But you do need a lot of space for these trees, and they are best away from a house where their special form and foliage can be best appreciated. They can break and shed limbs more than some other trees, so they are not the best tree for close to a house. --Spruce

"So, do I prune 1/2 of the material on the 2nd & 3rd leader, now (dormancy)?" Now or anytime before bud break in the spring. "Then wait until mid- Summer to trim-off the new growth since Spring, plus 1/2 of the older growth?" Trimming the new growth back is what matters most when keeping those branches stunted. Trimming the old growth back more is optional but not necessary. "Then follow-up with removing the rest or entirety of the 2 unwanted leaders next Fall or Winter?" Hopefully the middle leader will take over, fatten up, and fill in a lot this summer with the sides staying cut back. Then ideally, you can remove those branches completely next winter. As for the 25%, 40%.... I think it's best to prune trees in stages if possible. Typically in the summer, I will remove low branches first after leaf out (or chop them back if they are needed for overall growth.) Then 3 or 4 weeks later I will corrective prune out forks and fix leaders. Another 3 or 4 weeks later I will do tip-backs if the branch growth is too long, wild, and droopy. This gives the trees time to recover between prunings and limits the likelihood of suppressing growth by removing too much canopy at one time.