As I said; you'll read the practical limit well before the technical one.
Even for old ANSI formatted pst-files the limit it between 16.000 and
65.000. It all depends on how many items there are in those folders too.
Custom views are indeed changing from folder to folder; that's why they are
custom views. If you need a consistent view, then define a view of your own
and apply it to the folders.