For any here that don't know much about apple tree pruning, I'll offer just a couple thoughts. (This will be old news to long-time regulars here.)
When any of us talk of pruning off the lower limbs as the tree grows, it's to "raise the canopy" above where deer can reach so they don't break the lowest limbs - damaging your tree(s). Many guys strive to make their lowest limbs 5 ft. above ground for that reason. Some of us with bears may try to have our lowest limbs at 6 ft. above ground or higher to avoid young bears just reaching up for the heck of it. But the pruning of lower limbs is done in stages, a few each year to avoid removing so much leaf surface that the trees get stressed. Leaf surfaces = food factories for the trees.
I've followed the advice of several university professors and some veteran orchard guys on here with our own apple and crab trees, which is - each year prune off the lowest limbs until you get to the finished height you want your lowest limbs to be.
The second part of shaping your apple trees for years of fruit production is training the limbs to have wide crotch angles, which are much stronger than narrow crotch angles. This is done easily by placing a spring-type clothes pin immediately above new, baby limb shoots that sprout off the trunk (leader). The clothes pin forces the new, tender limb sprout to grow outward first - establishing a wider crotch angle as it grows. Wider crotch angles will better be able to support fruit loads as the trees bear fruit. Narrow crotch angles under fruit loads will most likely sag and eventually break from the weight. Same with wet snow or ice weight. Training your apple trees while they're young to establish the "framework" of your trees is much easier than trying to re-hab bigger trees later on.
If you think of your "scaffold" limbs (the main, heavier, fruit-supporting ones) as rungs on a ladder, you don't want them too close. Most sources recommend spacing the scaffold limbs 18" to 24" apart to promote good air flow and sunlight getting into the tree's interior (helps with disease prevention and fruit budding). A thick, dense canopy doesn't dry out well after rains or dew. The lack of air flow and sunlight make it easier for disease to set up camp in your trees.
MOST pruning advice out there is for commercial orchards that make their living from the trees. I asked the head of Penn State's fruit tree dept. if we need to be that fussy about yearly pruning for maintenance on WILDLIFE TREES. He said we can maintenance-prune WILDLIFE TREES every other year or two, unlike what commercial orchards do. He advised pruning out damaged, dead, or diseased limbs whenever we find them, however.
These tips are from real experts - NOT me. I just pass them along since the experts' advice has worked well for our camp trees. The first steps are always the scariest!!