CBSubs use case on a new project

Users buy a monthly or annual subscription, say 1200 $ for the annual subscription (or monthly payments). This subscription allows them to use a component which consumes credits (say 100 credits is included by default at the start, for instance 1 credit is used each time that they post something)

Then regularly and according to the frequency of their uses, credits are recharged and billed to their accounts when a low level is reached.

What would be best would be different levels of automatic recharges like 100/1000/10000

Is that feasible with CB Promotions ? and how ?

That is not doable. As stated earlier CBSubs does not support manually billing a user like that. It is a subscription management plugin. It is not an invoice/billing plugin. It is unlikely to ever support this functionality as it's outside the scope of the plugin. My earlier suggestion was to allow buying a CBSubs plan with points, which was due to me misunderstanding what you were wanting.

Last question : would it be possible to have a yearly plan A subscription and a sub plan B subscription/purchase that adds 10000 credits/points to a CB field and an autoaction decreasing this CB field by one or several credits/points at each definite action (like posting a photo) ?

That would be an alternative if we could do it that way

would it be possible to have a yearly plan A subscription and a sub plan B subscription/purchase that adds 10000 credits/points to a CB field

If they're both recurring then no. You can't combine 2 recurring plans with different durations in a single purchase. Most of the gateways we provide don't let you split up the purchase. If at least 1 is non-recurring then yes that'll work fine. CBSubs Fields can be used to increment your field when a purchase is made.

an autoaction decreasing this CB field by one or several credits/points at each definite action (like posting a photo) ?

Yes, use a Field action to adjust the points field.

Only Plan A would be recurring on an annual or monthly basis.

Can I use a merchandise plan for plan B or should it still be a subscription plan ? in order to use a CB field

Can I use a merchandise plan for plan B or should it still be a subscription plan ? in order to use a CB field

All plan types, including merchandise, should work fine with CBSubs Fields. Merchandise plan is also safe to purchase at same time as a recurring subscription since non-recurring plans are paid upfront so they can't conflict with recurring durations.