I would export your current OF DB as a OF document, then you can still open it (side by side with a new database) for reference, but starting over if you’ve been using another task management system might well be best - or importing the contents of your Things DB into a clean OF DB will be a better start than a mix of things anyway.
As a personal rule I only assign due dates if there’s a consequence, e.g. Library books have to be returned or renewed or I need to pay a fine. This page of the web application I’m writing needs to be finished by 2pm Monday because at 2:30pm I have a meeting and we need the page. “I want to get this done ASAP” gets a “Next” tag and sits in my Forecast view 