Great job on exposing some important things to watch for. I just posted 2 very in depth numerology post you may want to check out.

Just wanted to clarify a couple things as well;
-As I understand it, the term gematria specifically applies to relating numbers to words/letters. This is numerology. I believe dropping the zeros / adding the single digits until 1 is achieved is referred to as reduction. This is what my research has shown. To be very clear, this takes nothing away from the great work @jonexarmy 's done here. We all need to work together to decode this and to work together it is important we use the terminology correct.

666 reduces to the number 9, you've said is the number of Lucifer. In my research I have tied this number directly to representing Satan, do dark occultists consider Satan and Lucifer to be the same concept? Something I will have to research. I know off the top of my head the number for Skull & Bones is 322 (clever play on 666) and they definitely incorporate the idea of Lucifer, so this does tie the number to that concept, in at least 1 example I can think of.