Hi Gilly
Unfortunately the micro entrepreneur scheme (as it’s now called) excludes creative artists and writers. (It wouldn’t work because of the earnings pattern - ME is based on regular declarations and payments, but in the creative sector the earnings pattern tends to be irregular, you might sometimes spend a long time creating and earning nothing except maybe a few royalties, then you sell a work and receive a big one-off payment that might be significant proportion of annual turnover).
This recent thread may help
Is it safe to assume you have an EU passport? If so, basically the arrangements will depend on how established you are (ie how much you earn from your work) and thus what type of membership MdA gives you. But your first step in either case is to obtain a siret number (business registration number) from URSSAF in order to be able to promote and sell your work in France.
Healthcare might be trickier. The potential options are: 1. join PUMA after 3 months’ legal residence, and to do this you would need to prove a regular sustainable income and then pay an annual cotisation based on your total income; 2. access the social security system via Maison des Artistes if they accept you as a full member, and pay cotisations based on your professional earnings; or 3. take out private healthcare. The first two options will get you a social security number and you can then take out complementary cover via a mutuelle if you wish. The third option won’t get you a social security number, and hopefully you would only need to do this as a stop gap until either you are accepted as a full member by MdA or you’re accepted into PUMA.
Hope this helps, sorry if I’ve made it sound a bit complicated but artists and creatives are treated a bit differently from other professions in France.