Starting with: Should you wear a mask when out and about?
Yes. See this post from Daring Fireball's John Gruber. "We’re waiting for peer-reviewed studies. In the meantime, early studies and anecdotal evidence from countries with established mask-wearing social norms suggest quite strongly that mask wearing is effective." (May 21, 2020.)
See also "HAMSTER RESEARCH SHOWS MASKS EFFECTIVE IN PREVENTING COVID-19 TRANSMISSION" linked to and summarized by John Gruber. (May 21, 2020.)
John's not some conspiracy theorist. He's a respected tech blogger linking to various respectable sources of information.