Are AGIRC and ARRCO obligatory?

In June 2013 we registered our small gite business online, NAF code: 5520Z - Hebergement Touristique Hebergement Courte Duree, and am now in possession of our SIREN / SIRET numbers via INSEE. We also have confirmation of our registration with the local tax office. We have been tax resident for several years and are early retirees. We opted for the micro-BIC fiscal system and elected to pay our tax / social charges as they fall due, on a quarterly basis. An income stream began immediately following the registration date. By the way - the covering letter for the pension adhesion came from KLESIA.

1. We have now received a certificat d’adhesion and some forms from AGIRC and ARRCO regarding our pension contributions. I assume these are obligatory and do I need to fill in any of these forms or respond in any way?
2. There is a summary of charges (taux par tranche de salaire et regime recevant les cotisations) for both ARRCO and L’AGIRC et de l’ARRCO. Are these payable now and how do they know the levels without having declared any income as yet?
3. Is my gite income regarded as a salarie?
4. I know that there will be a delay before we declare our first tranche of income, which I hope to complete online. Do I need to register somewhere or is it automatic, i.e. do they contact me with registration details or a demand for me to declare my first tranche of income?