You do not rack up FF miles for train.

sfo traveler makes a lot more sense.

Florence may be so crowded as to not be worth the trouble.

as sfo suggested, but did not mention, the US-FCO, VCE-US open jaw will probably cost the same as a US-mxp or us-fco rt.

most of the lines will be so long that you will only be able to get on one ride each day. i.e. uffizi, st. petes(or is it paul?), doge palace.