Hello dkirving,
Three destinations in a week would be super challenging, but given that one is an island and CT is a bit of a logistical challenge makes these three in a week too much to try.
Depending on your transportation to Geneva you might be able to do Florence and CT but I might suggest something like the Italian lakes - which are already on the way to Switzerland - instead to maximize you time on the ground versus travelling between places.
There are flights to Sardinia from Florence so you could conceivably do (FLR) to (CAG) in the south or (FLR) to Olbia (OLB) in the north but I would take a careful look at what you want to see in Sardinia and what time that would take.
I would put down the number of actual nights you have and figure out how you're getting to Geneva to determine how many days you actually have and then work a schedule into that timeline including the travel between each place.
Sounds like a fun problem to have,
=Tod