1. I never had a problem doing so.
2. I'd say no. I do it all the time.
3. Depends what you call a shelter. A tent, generally no. In some places it is possible but between 7pm and 7am, and the tent must not be too tall, I think 1.2m max. Not sure though, search for other sources.
4. I do it all the time.
5. No problem.
I operate portable with my friends pretty much every other week-end and do exactly what you describe. I never had an issue. We have been "checked out" by the gendarmes a few times, as well as national park police. They just wanted to know what we were doing and were even somewhat interested... Mostly wanted to know if we could listen to their radios, LOL.. We were kicked out once off a site, abusively... Since then I carry park rules with me, on paper, to show them there are no restrictions about radio. The only thing they don't like is drones and 4WDs in many areas. We never had to deal with municipal or national police, but I suspect they would be more trouble. The gendarmes are very professional (military). Usually we don't see any uniforms...
Where are you going in France?