Some of my un-branched whips have just about dropped all their leaves. How soon can I cut tops off to get buds for laterals going?
Also on my other trees, the first scaffolds are only about 18 inches short of the central leader. Should I cut back half the vertical length there?
Not sure what you’re asking. Do you want to end up with a open center or a central leader? And if you know the rootstock that would be helpful.
I want a central leader. I want to say it is on M.106, but maybe M.111. Currently it is just a 48" stick with a bushy top and no laterals at all.
The other is a year older and has 4 perfect first scaffolds, But the scaffolds are to tall.
If you want a central leader then i wouldn’t do anything more than notch above the buds where you want to encourage branches to grow. Many examples of this can be found but I really enjoy Skillcult’s videos on youtube.
Try this one https://youtu.be/KAHNbjoTWyc?si=AhF-uLT21ncOF9Zo
Ah. I will give the notching a try.
Back to the other tree; how far do you prefer pruning the first lateral scaffolds? Should I take out all vertical growth?
Scaffold height is merely a preference for your picking and pruning circumstances. Im in an area with deer pressure so I train my scaffolds higher than most. The farther from my house, the higher I train them, otherwise the deer will just do it for me.
No deer pressure here. I’m figuring 6-8 inches should be ok.
If you don’t want to lose the length of the scaffold, consider tying it down. This will encourage the older wood to begin forming fruit buds and it stops the lateral from competing with the central leader. If it’s too long you can prune back the one year old wood (in your case the scaffold may be all one year old wood) but leave a couple of the young buds for the laterals continued growth. Orin Martins’ videos are pretty decent, YouTube channel: UC Santa Cruz Center for Agroecology
Posting pics of a couple of your trees would also be helpful for future newbies. 
Here’s a short three paragraph blurb on notching and a nice closeup of how much to notch.
Notching and PGRs to induce branching in newly planted, non-bearing and bearing apple trees | Tree Fruit Horticulture Updates.
A couple years ago… i bought a Novamac apple on B9… and it arrived with significant damage to the outside of the box.
Once opened… it was a nice long (4.5ft whip).
The top 1.5 ft of the whip had been broken beyond repair.
So… i pruned off the damage just above a nice bud at the top of the good wood.
That is basically what you were considering doing.
What it did… from that top bud initally… it set a nice cluster of blossoms… which i pulled before setting fruit.
Then over that first growing seasion 5 shoots/branches developed all in the top portion of the whip (top 5-6 inches).
Think that is mainly the problem with heading off a whip… you then get a bunch of shoots/branches in a small amount of space near the top of the whip.
Ideally your scaffold branches would have more distance betwen them.
I ended up espellar training mine and that is working fine so far.
