According to LDS is there a fixed and finite number of human beings?

> D&C 93:29 Man was also in the beginning with God. It has been presented in the comments here that one LDS belief is that "*there was never a point where we did not exist. We grow & develop, but do not begin or cease to exist.*" I do not know if this is an official LDS doctrine or simply the personal belief of one studied LDS adherent. Perhaps that is question #1. Follow-up questions would be: #2 Does this belief indicate the eternal existence of each specific, individual human being or some sort of notional existence of each or of mankind as a whole? #2a Prior to birth on earth is each human being spirit only? #3 If so, was there a fixed and finite number of spirit human beings in existence prior to creation? #3a If so, does depleting this number through the process of birth on earth usher in the end of the age? #3b If not, does the end of the age leave some number of human beings bereft of a body for the rest of eternity? * Apologies if I have not formulated very clear questions but this subject matter is not something I have ever entertained before and I have tried to be careful to limit the battery of questions that exploded into view :-) An ancillary question underneath or over top of this all would be; Is there any Biblical substantiation to this doctrine in the LDS view or is this purely new revelation? Related questions: https://christianity.stackexchange.com/questions/62287/lds-belief-in-pre-existence-of-the-human-person-vs-human-physical-deformities https://christianity.stackexchange.com/questions/4620/what-does-the-lds-church-teach-about-the-pre-existence-of-each-person-prior-to-c