Connecting in series is pretty much the norm in the german speaking countries and spreading throughout the rest of Europe. Even the French seem to be converting. The danger of a climbing smacking in the wall is considered a higher risk than a bolt failure. The ENSA made a video about it https://youtu.be/eqZQnCGl24A

Overhand seems to be good enough for most things, that how we connect our prussiks and they seem to hold fine. Just make sure it has a nylon sheath. Dyneema can be slippery. Girth-hitch seems to hold fine too, even when only one side is loaded.