A wheel = rim+spokes+hub. Are you buying a wheel, getting somebody to build you a wheel or building it your self?

Give us a picture of the Mezzo, at present I do not remember what the bike is like. Is there space for the new hub?

New chain is cheap compared to what you are doing here, so new chain it is. Is the old hub a IGH?

Question 5 is a funny one. It depends on the casette/front chainring you use. Maybe buying another bike is easyer/cheaper? If not take it to a shop. f you want to be involved in doing it (more than just paying for it) I suggest you read- alot in the mechanics and folder forums first.