1. Like any Italian phone owner phoning in France it will work but you will have to pay the international roaming tariff. That's 2 to 5 times higher than the normal national one. That might be acceptable for a holiday, but if you start living in France it's cheaper to buy a French SIM-card.
2. The minutes aren't on your SIM-card. They are on a Vodafone server. The small print of your contract says how long the are valid (or: have been valid). They might have a phone number (like 1200 or 1244) that tells you.

Kees