@Joseph,
I’ll answer in order.
1. It’s a generational thing. Hence the title “Nossi Hador”. The Alter Rebbes Chassidim treated him the way (more or less) we treat our Rebbe, same goes for the Frierdiker Rebbe and the other Rebbeim. I’m not sure which things you mean by “attribute all these things”.
2. After the Frierdiker Rebbes passing, a Chossid asked the Rebbe how we should continue writing to the Frierdiker Rebbe if there’s no answers anymore. The Rebbe answered him, “place your letter at the Frierdiker Rebbes Tziyun, and the Frierdiker Rebbe will find a way to answer” sometimes we’ll see an answer, and other times we won’t. The Rebbe during his lifetime didn’t answer every single letter either.
No, letters don’t drop from Shamayim, and finding letters and deciding that they were written to you specifically (opening Igros at random) was never instructed by the Rebbe.
Letter read by the Chuppah: I’m not sure what there is to understand here. Simply, the Rebbe would write a letter with the same standard text to all Chassanim and Kallos, and after the Rebbes histalkus, now that we don’t get a personal letter from him, we simply read out the Nusach he would write. FYI, same goes for Bar Mitzvos and other special occasions.
3. Chilul Lubavitch isn’t an “official” Chabad concept, it’s just something people say. I’ve heard many Lubavitchers who don’t like that term, but regardless, the way I understand it is:
A Chilul Lubavitch is obviously a Chilul Hashem, but it refers to basically, bad PR for Lubavitch in particular. It means when our image is ruined specifically. Again, out of all things, I don’t know why this bothers you. You’ve raised it in other threads too.