Shalom, dear rabbis! As a Noahide, I know that the people of Israel do not pronounce the four letters of Hashems NAME (if you, HIS people, do not pronounce it, what about us, the people of the nations?), however, I would like to know: 1. if we, Noahides, can also use the authorized pronunciation, namely, Havayah, for Hashem?, and, 2. if there are appropriate times to use Havayah or not (using it only in Torah reading, reciting Tehilim, in prayers, in Bible studies)? Thank you.

As you probably know, we just say "Adonai" in place of the 4 letter Name during prayer, Tehilim, and Torah reading. "Havaya" is just a "nickname" we use when wishing to relate to the 4 letter Name, without saying it (it is those same 4 letters with a change of order). You can and should do the same.