Can’t offer any advice I’m afraid except to say, find out the correct procedures from official sources, such as the government website / URSSAF website / EU website / MSA website if you’re looking at agricultural work, and then plan around that.
The French system as regards healthcare was revised at the beginning of 2016 to make it more inclusive and flexible. As far as EU ressortissants are concerned it seems designed to be totally in line with EU directives on freedom of movement. Everyone who ticks the right boxes should slide into the system no problem, but anyone who doesn’t tick the right boxes, won’t. So you need to think it through logically so you know which of the various different routes you intend to take, ie what your status will be, because the boxes you need to tick depend entirely on your status in France. For instance you say
What exactly do you mean by “register myself etc” - register as what, and for what? If you mean, register for healthcare as an inactif, you’ll need to show sufficient pension/investment income coming into your account each month to make you self sufficient. I think they look for around 900€ a month. Perhaps you can tick that box but the fact that you are looking for work, suggests maybe not.
On the other hand, if you manage to get an employment contract then you are not required to tick the 3 months residence box, because workers enter the social security system automatically the day they start work and their employer registers them with URSSAF as an employee.
What I’m saying is, be very clear about the process, and not “clear” in the Theresa May sense. As far as CPAM is concerned the rules are very clear: an EU ressortissant is a pensioner in which case they need an S1, or an inactive in which case they need proof of income and proof of 3 months residence, or an employee in which case there will be a signed employment contract and the employer will have registered him/her with URSSAF. Or if they fit into none of those categories then they’re a visitor and not entitled to healthcare in France.