This requires a small cash course in Aristotelian Metaphysics. Essentially, Aristotle posited that things have substance and accidents. The substance is what a thing is, its underlying nature. The accidents are how that thing is expressed.
My favorite example to try to explain this is a chair. We know what the nature of a chair is, a surface used for sitting, but just in my house I can count about six different kinds of chairs. Each of those types of chairs would be an 'accident" of the “substance” of chair. This isn’t a perfect example, but I hope it gets the point across.
What Jesus did at the last supper, and what the priest does every day during the mass, is change the substance of the bread and wine to the body, blood, soul, and divinity of our Lord Jesus Christ, while allowing the accidents of bread and wine to remain intact. Hence, what we are consuming truly is our Lord, but under the accidents of bread and wine.
It hasn’t. You can see even in the Acts of the Apostles and other NT books that the Apostles had a clear understanding of the true nature of the Eucharist. “Therefore whoever eats the bread or drinks the cup of the Lord unworthily will have to answer for the body and blood of the Lord.” (1 cor 11:27) We have given technical terminology to what was then only understanding, but nothing about the doctrine itself has changed.
We also have letters from various contemporary officials (Roman and Jewish sources, I believe) which accuse the followers of Jesus of cannibalism, explicitly in relation to the Eucharist. An excellent book that has examples of this is Hostile Witnesses. That book is an excellent read, I highly recommend it.
I believe the word might have been, but I am unsure. As I’ve shown though, the understanding of the transubstantiation has been present since the beginning.
He has not again drunk wine so far as we’re aware. It is likely that this was an allusion to the general resurrection at the end of time, where the saved will once again be able to partake of the perfected worldly goods in the new creation.