How do I deal with the paperwork after registering as an auto-entrepreneur?

I recently setup business Teaching English as a Foreign Language (TEFL) business in France.

1. I received my unions de recouvrement des cotisations de sécurité sociale et d’allocations familiales (URSSAF) registration paper - Registration d’Affiliation au régime Auto-Entrepreneur. Do I pay contributions and why?
2. I received letter and registration paper from RSI (Rėgime Social des Independants). Do I have to use it as they sent me a nouvelle attestation de carte d’assurė social. I am already registered with Caisse Primaire d’Assurance Maladie (CPAM) and already have my carte vitale.
3. I received letters from Malakoff Mėdėric concerning rėgime obligatoires des retraite complémentaire. Do I have to take that, as I do not plan to have anyone but me working to teach English?
4. I reviewed letter from Registre des Professionnels 2015, giving me membership number and asking me to pay 334 euros as montant d’adhėsio. Do I have to register with them?
5. Le Service des Impôts des Entreprise (SIE) contacted to inform me that they require me to complete my dossier concerning my activities. One question on the questionnaire concerning how much area of my house I plan to allocate for my work. I plan to work at company offices or at student houses, not from my house.
   1. Can I indicate this on the questionnaire?
   2. Will they start applying business tax rate on my house?
   3. They want me to indicate who my accountant is. Is it obligatory to have an accountant?
6. Do I need to open a separate business bank account in France in order to keep any income I get from teaching separate from my personal bank account?