As for battery safety, I would suggest sticking to Sony, Samsung, LG, Panasonic and Shockli cells and buy them from reputable sources and use only good chargers. Others here will chime in with good EU battery sources.

Just keep your cells in a cool dry place and store them in the little plastic battery cases or something else that will keep the contacts separated to avoid shorting them out.

As for the battery bags, I do not see the need as long as you treat your batteries with respect. My first Li cells were protected pany B’s like you have. I was concerned about what COULD happen with a Lithium cell so I decided to go that way. Now I understand that if you treat them right, quality unprotected cells are the way to go and are safe to use.