During summer ball I see a lot of leaning in on free throws. What are your views on when is it a violation? If they break the plane before the ball hits the rim or do they need to touch across the line?

The book says it's a violation if the foot breaks the plane, but common sense tells you to call if by advantage/disadvantage.

So you think a little over the line is probably ok but if he gets a headstart should probably call. What about maybe calling it close early on so they get the point to wait?

Just give them a short warning about it while your admisatrating the shots. Then when you call it, they dont look so surprised ;)

This may stur up another pot of contention but what in the world does advantage/disadvantage have to do with leaning into the lane(unless contact is made with another player).
The only part of the body not allowed to break the 2x36 inch box (lane space definition) is the foot. leaning in is legal, leaning into another lane space is legal until it results in contact then you can apply A/DA. Leave A/DA out of violations it is meant for contact situations to determine incidental contact.

What about 3 seconds? You gonna call a carry on a kid in the back court with no defensive pressure, just because they went under the ball? You are officiating younger kids, on a bad court ( dusty, dirty, slick), are you going to call a minimal jump stop slide?

We have to apply the spirit and intent of the rules. That means all of them and just not contact.

do not confuse game management for A/DA. Lets use your carrying in the back court senario: JVHS and below probably
no call with a verbal, HS and above called, any level
in a blowout team behind no call, team ahead call. Officiate to the level of the play involved thats game management not A/DA. By the way In the 4 camps I have done this summer HS,College & ABA in 2 of the levels we were told the quickest way to clean up the post was to enforce the 3 second rule how about that for a change.

I disagree the higher you go the LESS likely you will call that carry. That and all the cases I stated are about A/DA.
Did the kid gain an advantage by palming the ball without a defender? No, A/DA.

If a young kid on a bad floor slides on a jump stop and it does not open up a shot, nothing. If they slide past the defender, travel. A/DA

I'm with blindzebra. Your case about the score difference on wether to call somthing or not is game management. But calling the carry or not is A/DA. Some cases could be both though.