Prayer

After counting the omer each night, there is a short prayer HaRachaman Hu Yachazir Lanu Avodat Beit HaMikdash Limkomo Bimheira Be'yameinu. Amein Selah Amen is the usual ending of a prayer. Why is the additional word selah necessary? What is the meaning of "Amein Selah"? What do the two words together mean versus each word separately? Thanks.

In a Sabbath service, is one supposed to bow when the word Baruch is recited since Berech means knee?

As we know, there are two main forms of Hebrew: Ashkenazi and Sefardi. And the most notable difference between them is the pronunciation of the last letter, the ת, as either an S or a T. Though the T-sound is considered Sefardi, I hear plenty of Ashkenazim using it. And I hear people who constantly switch around between the two, using them interchangeably, sometimes even in the same verse! (Example “YiTgadal V’YiSkadash”) How important is it to pronounce this letter according to one’s heritage? If one pronounces it differently from one’s family custom, is the prayer or blessing still valid? If a Torah reader pronounces it unlike his tradition, must he be corrected? How about if one suddenly decides to change because he joins a congregation that does it the other way or simply wants to?

Hi-- I'm trying to find out more about the Ana BaKoach prayer. I know it is traditionally said during Kabbalat Shabbat. Is there another place in our daily or weekly liturgy where I might find it? Do you know when it first appeared as a prayer? What else can you tell me about it? Thanks!