Before Napoleon there was no such thing as surnames, and everyone was called by 1st names, including Moshe Rabbeinu & Avrohom Ovinu in the Toroh, so clearly using a 1st name, is emulating the way the Toroh speaks about people.
Indeed in Gateshead Yeshiva the Rabbonim are referred to by their 1st names. Albeit with Rebbi in front, but so do family names, have a Mr. or Mrs. in front.
Only exception in the Toroh is calling one’s parents & ancestors, so this is my guideline too.