Maybe things have changed, but I have never needed an IDP. They always wanted my state or provincial driver’s license.
About 50 years ago, I lived for a year in Switzerland. The town I was in had a traffic circle at the center which operated by priority to the right. In rush hour it was totally clogged since cars coming on to it had priority. They used a cop to direct traffic and keep things moving a little, but was hopeless. When I spent a few weeks in that town about 25 years ago, I observed that now priority was given to the cars on the circle and now things operated smoothly. Cars coming on were blocked until it cleared, but traffic moved.
A debit card with a chip as you described should work - likely contactless, so you won’t need to input a pin. Signs above each toll gate will show you which are card only, card or cash (automated), or booth manned by an actual human.
Automated machines that take cash will take notes and coins, and will issue change, so don’t worry about that (pic), Larger toll intersections will also have manned booths.
Droit is straight, droite is right - similar, but not the same. Are you worried about signposts? The arrows make it pretty clear, I wouldn’t worry too much.