Unfortunately I think here is still no way to see where your page break will happen in the Pluto notebook.
There was a contribution in a PlutoUI issue on how to create custom pagebreaks in cells so that you can control a bit the printing flow.
For what regards changing the width of the notebook, you can do that by putting custom CSS in any pluto cell.
For example you can always center the notebook and enlarge it by adding this
html"""
<style>
body:not(.disable_ui) main {
max-width: 95%;
margin-right: 0px;
align-self: center;
}
</style>
"""
to any cell like so:
and the export to pdf should also print with wider cells.
There was also this package:
specifically made for customizing the Pluto appearance