So, I was wondering two things:

1. Does the ID need to only be unique within the datapack, or do I need to be concerned about multiple quest datapacks being loaded at the same time and possibly conflicting with the other pack's IDs?
   and related to that:

2) What characters are allowed for an ID? Are they strings or integers? For example, could I make an ID something like "packname_fish1"?
Realized they're not in quotes, so they're integers. My bad on that one.

Another question, actually: is it possible to flag a quest as available to all professions?

Cool, thanks!

The quest id has to be unique to all datapacks.
the second question can be a feature request :)