How to add a second, smaller business (pottery) to the chambre d’hote business

My husband runs a Chambre d’hote as Micro Entrepreneur with about 80k EUR sales revenues per year, Activité Principale Exercée is 5520Z Hébergement touristique, opted for versement libératoire.

Now two things will change this year:
- He has started his pottery business (handmade ceramics) which he would like to sell as well (on-site to guests, and online through a webshop), estimated revenue for this year: max. 5’000 EUR, in the future it might be more if things work out
- I will move to France, too and will join the chambre d’hote business

How would you recommend to cover this new business?
1. Can he just add another activity to start with? If yes which one?
2. And would the social charges still be collected by URSSAF?
3. If the revenue with the pottery would grow, let’s say to 30k EUR per year, what business structure would you recommend? (to optimize social charges and income tax) Anything else to be considered?

If I join the Chambre d’hote business as a conjoint collaborateur,
4. Is there anything to be considered (also with regard to the new business with pottery)? Do you see any hurdles?
5. How much will the social charges rise (today he pays 12.4% of chiffre d’affaires for social charges, plus 1% for versement libératoire de l’impot)

Thanks a lot in advance