Approximately 3 - 4mm max. Otherwise open bite will occur. The plate will not keep the ink. If you do have a screen then of course you can use large solid black areas and get a nice results. The plate is reworkable with a drypoint needle or a mezzotint rocker, but as the film has hardened you need to be careful for it might chip off. I have experience with ImageOn HD and DK films.
Line drawings do not need a screen to hold ink but need to be as opaque as possible to guarantee the best quality of line.