Eligibility criteria for naturalisation are relatively straightforward, the biggest hurdles for you are going to be:
Gaining the visa / residence permit in the first place
Having a stable job (required for a talent visa anyway but often an issue for people on another kind of visa)
Beyond that, you need to reside in France for a few years, know basic French ...
Yes. You can stay in the US as long as your OPT is pending. Time before your OPT is granted, as shown on your EAD, will not count as days of unemployment. See the OPT policy guidance:
7.1.6. What counts as time unemployed?
Each day (including weekends) during the period when OPT authorization
begins and ends that the student does not have qualifying ...