Pricing and billing

I am working on a solution using Typeform for one of my clients, and trying to work out the best pricing plan to be one.  We are creating a short-term marketing campaign where we will be emailing ~150k historic Customers, directing them to come and check out an offer, and hopefully purchasing a ‘membership’ via Stripe.

I can see the top plan (Business) allows for 10k responses per month….what happens when you breach that?  Will the survey be unavailable after that limit is reached, or will it bill us at an additional rate?

It’s hard to know what our likely response rate will be (this is a new proposition so we aren’t completely sure of the appetite in our customer base), but I guess we could stagger the campaign, and stop once we look like we’ll hit that in a given month?

Any advice gratefully received.