Turn on auto-size columns in Settings > Folder Options > Display tab or Settings > Preferences > Folders > Folder Formats.
If it doesn't work for some reason, also see this post: [Auto-size columns not working)
And/or have a look at the Folder Formats FAQ: [List of FAQs organised by topic)
I don't think you can turn auto-size columns on and off with a hotkey ...
But you could create a button with this code (see help file):
SET AUTOSIZECOLUMNS [,dest,left,right,both,focus,widest]: This command automatically resizes all displayed columns in a details or Power mode Lister.
It is the equivalent of double-clicking on the separator bars between each of the column headers.