Menachem, I’m impressed with your ability to find sources for things. I still think there’s a difference between what one rav says 100 years after the baal hatanya, and what the consensus of gedolim were and are regarding the gaons treatment as a rishon in halacha. Do chabad yeshivos teach shu”a harav as a rishon? It’s fine with me if they do, but that’s not what the rest of the Torah world does in practice.
Someday, you can find sources for that sentiment in rabbi reuvein schmeltzers sefer on emunah(the English one), he has a whole section on how you can teach emunah to children through stories of gedolim, and spends a great deal of time on the gaon.
Re, the ramban and rambam, you’re referencing rav chaim volozhiner in the back of ruach chaim, where it says that some were saying that the gaon was on the same level as the rambam, and rav chaim said “definitely not the rambam, maybe like the rashba or the ramban.”