Hello! For the limited quests, characters can sign up for more than one of them at a time, but they're not repeatable.

For the resource quests, you're correct, characters can repeat these as many times as they'd like! However, they will only gain points from those once per month, so you don't have to report them doing the STONE quest multiple times, for example. You can, however, thread it as many times as you like, or write in tags how they're doing that, etc.

Hopefully that makes sense!