Mod 42: I’ve thought about that for a long time, and I think I know where that Minhag comes from. The Halacha is technically that one should (Min Hamuvchar, if someone’s tired or has to get something or whatever there are three levels) wait until Kedusha to take their three steps forward. Also, Nekadesh was originally an introductory line by the Chazzan (at some point the Minhag changed to make it part of Kedusha). Thus, people would take their three steps forward right into Kadosh Kadosh Kadosh.
Oomis: The left, right, and forward thing is I believe mentioned in Sefer Chassidim (but I could be mistaken, he might only mention that you need to bow while taking 3 steps back). And it’s clear in the Shulchan Aruch that you need to take 3 steps forward before starting Shmoneh Esrei. My point was that it has to be before you start, not during the words “Hashem D’fasai Tiftach”.
BaalHabooze: I once had a Rebbe who taught us that Unlce Moishy’s “Hashem is here, Hashem is there…” song is a violation of the Ikkar of the incorporeality of HKBH.