F1 hotels are basic but fine for just getting some kip. Make sure you have your crit air sticker on for France. It comes quickly so order today. Not sure what the other countries need for windscreen-stickers.
Tags are handy for tolls, but I have always had a passenger so less hassle for RHD.
Garda – there are campsites in places like Riva del Garda, but it’s busy. A nice nearby quieter alternative would be Arco. Arco is lovely anyway by comparison and a bit inland, hence less busy.
Driving in Italy is a little hairy, but you will get used to it. Driving in France is far easier than driving in the UK. I haven’t driven in Germany though.
Not had issues with supermarket fuel.
Don’t speed.