Re: classic and medieval latin
Not many differences at all.
Since the time of the early Roman Empire, Latin changed very little. The most prominent changes in Latin occured from the late republic thru to the early empire.
Latin was re-borne in the medieval period in scholarship primarily for the purpose of reading ancient Roman texts, so Medieval latin catered to these needs. Latin was then expanded in the Medieval period as a language of science, philosophy, and law, and because of this there was an expanded vocabulary and it's believed that some pronounciation may have been different, but all in all very similar. Aside from the odd new added jargonistic words, the syntax and lexicon was really quite similar to Classical Latin.
None of this of course is to be confused with Ecclesiastical Latin, which was, and still is, the Latin used by the Catholic Church that is distinguished with a much reduced vocabulary, a much simplified syntax, and some lexical differences. In fact, Ecclesiastical Latin is really quite similar to Vulgar Latin.