Are the sub-account limits are based on the main paid account limits?

I have sub-users assigned under my paid account are the sub-user accounts treated like a free account or do they share in my paid limitations based on my plan?

Yes, see to it that the forms they create will be under your account which is the folder they see under the "Shared with you" section. For example:

If the My Forms section is present in the sub-user account and they will create the form there, the limit will be based on the Free Plan.

Let us know if you have any further questions.

Thanks