Best time to visit
It depends on what you have in mind. If you want to go to the beach, May to September are ideal. You can go on a city trip all year round. For skiing, you should arrive between December and March.
Driving
A national driving license is sufficient for EU citizens. The road network is well developed and the roads are usually in good condition. The traffic signs and rules are largely standardized within Europe.
The speed limits are 130 km/h on freeways, 110 km/h on motorways; 80 km/h outside built-up areas and 50 km/h within built-up areas. The blood alcohol limit is 0.5 per mille.
You can find more information here.