hello. In general, autumn is not the best season for birding in Italy, as it's prime hunting season. This means that in some parts of Italy (all of central Italy, the provinces of Bergamo and Brescia near Milan, and some parts of the South) most of the countryside, apart from protected areas, will be open to gun-toting half-wits who shoot at anything that moves. This said, there might still be scope for birding in nature reserves and wildlife sanctuaries.
Migration will be in full swing by then, so anything may pass by. I don't have much advice for Sicily, although I suspect that the Trapani saltpans, not far from Palermo would be a good bet. If you need more info on Sicily, you can send me a PM and I can circulate your RFI to the EBN Italy mailing list.
Rome has some coastal reserves nearby which can be very good during migration. You will need your own car to get there, but you can ask the
GROB people for further advice gruppo_romano_birdwatching at yahoo groups dot com.
Florence has the nearby Piana Fiorentina with a couple of protected wetland areas:
http://www.wwf.it/oasi/toscana/stagni_di_focognano/, and
http://www.zoneumidetoscane.it/it/le-aree/la-querciola-sesto-fiorentino/lambiente. Or there are a few coastal reserves near where we are, but you would need to set aside a full day.
As for Venice I would set a full day apart for visiting the Po Delta National Park, which is the most important wetland system in Italy
http://www.parcodeltapo.it/pages/it/home.php. We know the Emilia-Romagna part pretty well and we visit very couple of years or so. You can read our report from the
last time we were there. We have been only once to the part north of the Po river, but you can find some information her:
http://www.parcodeltapo.org/index.php/it/. My only word of advice if you go there is: don't EVER leave your car unattended with valuables in it while you are in the Po Delta area, as it is infamous for car break-ins. Thieves know that birders come equipped with expensive optics and they are FAST and know what to look for. Always take your valuables with you. We have never had problems but know people who have lost all their gear.
If you need further info do PM me and I'll be glad to help.