Going from employed to micro-entrepreneur or enterprise individuelle & when to start

I am moving from a fully employed to a Spanish company with Spanish residency to freelancing for the same company but from France.
I understand to have the full benefits I should set up a SASU, but to start with a minimum viable product I am thinking to start with microentrepreneur status or maybe enterprise individuelle. I know this will affect my social security benefits and for that I plan on taking private insurance.
I do service based work, product development (Product owner) within the software industry. I will have one single customer whom is based in Spain, while me, I will be based in France. As a business I do not have much of cost, do not need to purchase equipment, occasional business trips.

1) As legal status, would micro-entrepreneur cover my situation, for at least for the first 1-2 years? (I know I will exceed the limit of 72000€ revenue) If not, what status would you recommend would suit my situation better?
2) Linking the topic to social security, I understand a temporary social security number will be issued, within 2-3 weeks, as part of the process of setting up freelance legal status. This temporary social security number than will serve to start visiting the doctors in France, but my doubts are: could I start my activities right after setting up the legal status, or do I need to wait until the temporary social security number is issued?

Many thanks in advance