Vim 80 column layout concerns

The way I do 80-column indication in Vim seems incorrect:set columns=80.
At times I also set textwidth, but I want to be able to see and anticipate line overflow with the set columns alternative.

This has some unfortunate side effects:

1. I can’t set number for fear of splitting between files that have different orders of line numbers; i.e. < 100 line files and >= 100 line files will require two different set columns values because of the extra column used for the additional digit display.
2. I also start new (g)Vim sessions instead of splitting windows vertically. This is because vsplit forces me to set columns every time I open or close a pane, so starting a new session is less hassle.

How do you handle the 80-character indication when you want to set numbers, vertically split, etc.?