S1, social charges and micro-entrepreneur

I am 69 and am retiring to France this autumn - I am ready to request my S1 so that I can request a carte vitale from CPAM on my arrival in France. My wife (who is French but who has lived abroad for 25 years) is 49 and she will take a career break for six months when we first move to France, so I had intended to include her on my S1 and carte vitale so that we can both benefit from health cover. We will become tax resident in France, and I understand that my UK pension income would be exempt from social charges and would only be subject to French income tax, levied on our household income.
At some point in 2019, my wife will probably want to return to part-time work - perhaps letting out accommodation adjacent to our house, and perhaps acting as a bilingual sales agent for an estate agency - maybe both. She is considering doing this as a micro-entrepreneur, and presumably would therefore be entitled to a carte vitale in her own right. Our questions are these:
1. What earnings as a micro-entrepreneur does she have to make in order to receive health cover in her own right?
2. If she did get her own carte vitale as a micro-entrepreneur, does that mean that I would have to be linked to her card? I am keen to keep my carte vitale linked to my S1 in order that I do not have to start paying social charges on my pension income.
3. Could my wife stay linked to my S1 even if she was earning as a micro-entrepreneur?
4. Would it be preferable from the start for each of us to apply for our own carte vitale cards separately - me via my S1, and Pascale via her role as a micro-entrepreneur, even if she did not anticipate any earnings until 2019?
Thanks for your help.