Each guy has their own situation. If you don't have many deer, you might be able to get away with tighter cages if browsing isn't a big problem. But a few deer can eat a lot !! We use 4' dia. cages and have had some branch tips chewed, but it hasn't hurt the trees. As they grow taller, we prune the lowest limbs off so the lowest scaffolds are 5 ft. above the ground - or higher. We have a fair number of deer and this method has kept our apples & crabs 95% free of deer nipping.
Aluminum window screen height depends on how deep your snow typically gets. I use 32" wide screen (off the roll) and cut pieces 18" long, so when I fold it in half around the trunk to staple it, I have 9" on both sides. Then I just staple it shut and have a sleeve 32" high X 9" wide, with "slop" room inside to allow for trunk growth. This gives us protection if the snow gets 30" deep or so. As others have said, we also pile crushed stone around the base of the screen about 4" deep so mice/voles don't want to tunnel through that to get inside the screen.