Why did the Rabbis change the celebration of Shavuot by counting 50 days from Nisan 16 instead of 50 days from the day after the Shabbat following Pesach as indicated in Levitcus 23?

I am an orthodox woman who was taught that intimacy with a husband is not only allowed, it is ecnouraged and a big mitzvah. I've been also told, and read (in reliable sources) that relations are not only a big mitzvah, but "kodesh kodoshim." Although I definitely enjoy being with my husband and giving & getting pleasure, I cannot see why it is so holy? I understand that it's allowed, but to call it holy of holies? After all, it's pure physical pleasure- what's so spiritual about that? Thanks!

Does the Neshama itself get "sulllied" or impure when a person sins, or since it's a part of Hashem it remains pure and only the sinner gets impure ? If so, how does Teshuva erase the "dirt" of the sin?

Shalom Rabbi, Why do such horrible things happen to the children of the world? Why does G-d allow such things to happen? Thank You...I am struggling right now.

I was talking with a Rabbi when an interesting question arose. If a young man (in his teens) already has a full beard, is it permissable for him to shave or trim it until he has reached the age of 20? Also, is it permissable to put a bulletin board in a Shul so long as its purpose is religious?