Hi Tob,
Do you have paper maps, and have you decided exactly where you will be walking yet? I imagine there would be many ways of walking to Rome from there...
I put your start and destination into Google maps, and it
came up with this. Not much help! At least they didn't suggest a Sea Kayak

Seriously, if you know where you want to walk, getting it onto a GPS shouldn't be too much of a drama. If you don't know then you need to work that out first.
I've not walked in Italy, but I have been near the start of your walk, but on the Swiss side of the border, so I know a little of what it looks like.
Cheers