Firemac -
Reviews of vacations, hotels, resorts, vacation and travel packages - TripAdvisor is your friend in these matters. I would suggest you take a little time to research this site. Make sure that your hotel is relatively central - whilst Florence is easy to walk around, there are plenty of hotels quite a way out of the city centre. It's a great place, hope you have a fantastic time.
Oh, and don't worry about the train bit - it's dead easy - the station in Pisa is almost literally outside the exit doors of the airport and the station in Florence is slap bang in the city centre.