questions about the Hebrew language

Yes and no. Hebrew wasn't a lingua franca, per se, but it didn't completely die out among religious Jews. For sure, it wasn't anyone's mother tongue, but it was learned by all Jews who stuck to Judaism, and it was useful for communication with other Jews who didn't speak your own language (both Yiddish and Ladino eventually came to supplant Hebrew as "Jewish languages" among those who shared a common heritage). Hebrew was used for writing ethical tracts (such as Mesillat Yesharim (R. Luzzatto) and HaIkkarim (Yosef Albo)), legal codes (Mishneh Torah (Rambam)) and more. So it was never officially "dead," but it wasn't spoken as a mother tongue.

It was revived as a natively spoken language by Eliezer ben Yehudah, whose children were the first native speakers of Hebrew since about 2000 years ago. I don't know what books you can read on this. You might look through Rabbi Telushkin's books. They've generally got information about everything Jewish.

There were several attempts to develop vocal representation with written Hebrew. The system that we use was developed by the Massoretes and used in their copies of the biblical texts. This was around the year 900, if I recall correctly.

Without Ben Yehuda, there would probably be far fewer people able to answer this question.

Hebrew was maintained through the Middle Ages and into modern times as a language of religion, similar to the way Latin united Christendom.

As a casual spoken language, it did indeed die out, which may be part of the reason why the Masoretes under Ben Asher got into the business of recording the proper pronunciation of the OT. That happened between the 8th and 10th centuries. One of the oldest vowelized texts is the Codex Cairensis, containing the Prophets, which was written around 895.

When the question of a Jewish state arose, there was serious debate about which language it would adopt. For a moment, German competed against Hebrew for the language of Israel. Hebrew won out, for the obvious reasons relating to Jewish culture. Eliezer Ben Yehuda was most responsible for the development of modern Hebrew from it's Medieval and Ancient forms, and spread it throughout Palestine before the modern state of Israel was ever conceived.

I agree with Yonah, R. Telushkin's books are excellent.