Hi there, @Kate4 
I completely got your use case, thanks a lot for sharing the detail!
By the way, happy to say that the form feature is already available in our Calculator. Check this post for more details - Calculator: Send calculation results directly to email! 🚀
It means that now, you can send the calculation results to email and make the email field required for submitting the form:
Conditional results and a limit for the same email usage are not supported yet, but we’ll have these ideas in mind and see for more feedback from the community on the Wishlist 