Depends, when you ring is expensive or made from gold or silver it better match with elegant outfit. Casual clotting much better match with informal light accessories, costume jewelry made ??of semi precious stones, jewelry made with African or Indian motifs, pearls, coral, etc. :)
sure, you can. You should choose another casual clothing which fit to your ring more
I know a lot of people that wear a ring every single day, I think you can wear a ring with anything! I don't think it needs to match as long as it's small and not super fancy
I would wear it as long as it matches. Jewelry always makes an outfit better :)