We went with Italian friends from Oxford to Florence the other year.
The most important thing to realise is that it's a bloody long way - about 1000+ miles depending where you are going!
We did Oxford to Turckheim, just outside of Colmar in France, followed by Turckheim to Florence. They have done this route often and reckon its the most comfortable.
Route was via Dunkerque, to Belgium via Charlleroi, across Luxembourg (where petrol is cheapest) and then back into France via Metz into Alsace.
Alsace is lovely in the summer - you could stay an extra day and visit, there's enough to do and see - can even wander over the border to Frieburg and the Black Forest.
Then onwards via Mulhouse and Basel into Switzerland, Lucerne and the tunnel (St Gothard I think - 20 odd-km was glad when it was over) and into Italy via Lugano and down to Milano on to Tuscany.
As previous folks have said, it's cheaper via Switzerland - you can buy toll passes for the motorway at the border in Mulhouse-Basel.
Headlights during the day ? Maybe if the weather is bad but otherwise not - maybe there are new laws in Italy but not elsewhere as far as I can see (like France last week).
Yellow jacket in France is now obligatory if you break down - must be in the passenger compartment of the car, not the boot, first aid kits in Germany, and full set of replacement bulbs for many places. Triangles usually not needed if you have hazard warning lamps and are not over 3 tonnes - although this is subject to change of course.
Good places to stay en route - in France look at "Logis de France" on the web, good no-nonsense hotels often with a restaurant. Probably best value for money on the whole ride - it's what we usually do
On the whole driving was good - Belgians are a bit unpredictable, French are OK in general on the autoroute, Switzerland was fine, Italians were in a hurry but generally OK.
But as honorary French person and French driver I'm probably immune to lots of things
If the weather is good, the scenery is fantastic - so enjoy