On the free plan is 100mb limit per month? if the limit is reached and the forms stop working does it refresh and is usuable the next month?

The allocated 100MB storage upload space does not reset to zero (0) on each month. 

Unlike the form submission counts, resetting the 100MB storage space will meant deleting existing uploads/files on the account. So this is not done automatically.

Yes, if the FREE account exceeded the 100MB storage space allotted, it will temporarily disable further submissions on the forms. It will require upgrading the subscription to a higher plan to get an expanded or bigger storage space allocation.

You can review the subscription packages here https://www.jotform.com/pricing

Hope this help. Let us know if you need further assistance.