Problem with registered activity and professional insurance

I started business as a menuisier in France. My insurance broker has now told me that in order to be fully covered for all the activities I carry out I will also have to be registered as a charpente, including maison a ossature bois. He also stated that I will need a certficiate dans registrament from the chambres des metiers.

I’ve spoken to an English speaking advisor from the Franco-British Chamber in Brive who told me that some charpente activities (such as making wooden houses and roofs) can not be registered under the auto-entrepreneur, as they are considered to be too specialised and dangerous, and that I may have to change my regime. The person I spoke to at the chambre des metiers in Limoges told me (in French and my French is not great) that as an auto-entrepreneur I do not need a certificate dans registrament.

I’m very confused, and deeply concerned that I will not be able to carry out my first contracted job, which is due to start on 19th april.

1. How do I add additional activities to my inscription?
2. Do I need a certficate dans registrament?
3. How can I make sure that I am properly registered to carry out my first job in April?