is there a way to specify via the grid itself that the grid border lines should be visible

No.

does one accomplish this via adding border to the grid components (eg the cells)?

Correct. One way you can do that is to specify

    -relief => 'solid',
[download]

when instantiating your widgets.

what if the cells are of different sizes, and one desires a regular grid, like graph paper?

You have to calculate the size yourself. You either specify a size that you know is big enough for everything, or you get the size or your largest widget. Something like this untested code:

  # after you instantiate all your widgets in $master.
  $master->update;
  my $maxHeight = (sort {$b <=> $a}
                   map $_->reqheight =>
                   $master->gridSlaves)[0];
  my $maxWidth  = (sort {$b <=> $a} 
                   map $_->reqwidth  =>
                   $master->gridSlaves)[0];

  $master->gridColumnconfigure($_, -minsize => $maxWidth)
    for 0 .. ($master->gridSize)[0];
  $master->gridRowconfigure   ($_, -minsize => $maxHeight)
    for 0 .. ($master->gridSize)[1];
[download]

HTH.