Sometimes I start Vim by pointing it at a directory, but I'm not certain yet which file I'll need to change, so I end up looking through several files.
Is there a way to make the file browser open a selected file into a new buffer so that the file browser is still available without having to reopen it with :e path/to/directory ?
I'm not sure if you can have it open in a new buffer, but you can have it open in a new split using o or v for a horizontal or vertical split respectively.
You could also preview the file using p which runs :pedit <fname> where <fname> is the file under the cursor. This opens a new split window but doesn't change the cursor focus or position. You can close this window with :pclose or simply :pc.
See :help netrw-browse-maps for more information.