The class skeleton shall fit on a single page, as do all methods (including the private methods that are used by a single method only)

How large is my page? Good question, but this is not important. If my job requires this, I use A3 paper:-)

No, serious. There is no absolute measure how many methods a class should declare at maximum, our how many lines of codes a method may have.

If you have to scroll often to overlook your class or method it might point to a potential design flaw (note benchmark remark in the intro)! This applies of course to all method folded or the outline of Eclipse(for example).
There are bean-like classes with hundreds of get/set pairs - definitely a problem, there true methods, but the follow some “pattern”

initPersonHeader()
fillPersonHeader()
initAddresses()
fillAddresses()

Sometime these classes have the surname “Fa├žade” - a case could be made for that, but most of the time these classes need to be split. An API does not get simpler by having all methods on single class, nor does it get more complex if it is a bit more structured.

For methods the problem is the much deeper. Long methods do complicated things, but perhaps the work is not well prepared. Misplaced methods often have a tendency to outgrow, programmers use several private methods that just server as “macros”, while working around the fact that the class they are working on is performing something that doesn’t belong to it in first place.

This is also why I count private methods as being part of a methods implementation: Programmers cheat there, they create the illusion of structured work by calling dozens of private methods, but it still remains spaghetti.