Fire fighting! No passengers......
That's not granted in Italy.
Helops. Your first question should include the italian region you would go for firefighting and the operator you would go for charter flights.
In one region firefighting is usual finding yourself taking-off hot and heavy (and very windy), with bamby bucket, 4 "passengers" (engineer, Forestry Officer and 2 from Ente Foreste), all of them talking about your water drops, landing zones, and how better the previous pilot was and and bla bla bla
In another region you're alone with nobody even watching from the ground what you're doing. or arguing about how full is your bamby during the first launches, when your're still full of fuel.
At least, you can be pretty sure that your employer is an AOC holder.
About charter flights, the key is doing it in the most legal way. That's not aerial work. Your good homework with W&B, landing sites, flight planning, risk assesment, weather, managing flights from/to other countries etc will make the difference. If the employer operates in summer from a small airport in Tuscany you'll probably fly also over water... Am I wrong?
If you choose this option, you should aim for the twin.