1. Yes
2. Matilda Charlotte is fine. Don't care for Eleonor Charlotte. Charlotte would be better as a fn, imo.
3. I know one who is in her early 40s. I was acquainted with another who went by Char (which I detest). She would probably also be in her early 40s.
4. Lovely and classic. Sweet on a child and will age very well.
5. Charlotte Diana, Charlotte Rose (though Rose as a mn always makes me think of the verb form of rise... Charlotte rose from her chair...), Charlotte Gabriella, Charlotte Genevieve, Charlotte Helena, Charlotte Victoria