Upload & Sell: Off
Would it be safe to say import locally, work locally, then back up edits externally? No sense in backing up images unworthy of processing, right?
No - not safe.
Everything needs to be backed up to external storage.
Not everything needs to be edited manually because they may already be pretty good. These need to be backed up too.
Even poor shots can be worth keeping because they remind you of something that is now irreplaceable or they can inform you of problems with gear or technique (e.g. via the metadata). These too need to be backed up.
If it is worth keeping at all and you have not yet deleted it then it needs to be backed up. Everything that you would miss now or at any time in the future if it was lost right now should be backed up right now. The next backup should be to a different drive. And the one after that to yet another drive. Eventually you can start re-using old backup drives but don't keep all of your backups on a single drive. And you have to keep track of backed-up files that are no longer on your main working drives because the backup drive(s) may fail or be stolen.
Backing up is always an inconvenience but very likely a necessary one sooner or later.
If you have insufficient space on your internal drives then you can split your library by putting some of the less-used images onto an external working drive, but this is not a backup - it's just another drive to be backed up. Even those external image files can remain in the main Lr catalog, so there is no need to have multiple catalogs.