If I downgrade back to free, do I lose all the data from my current forms?

I need this service on a project by project basis, so the plan will be to upgrade again when we have the next project. The service works perfectly and I'm very satisfied with the results :)

No, you'll not lose the submissions. However, the free plan only have 100mb storage space. As of right now, your account shows you have 229.80mb upload space. If you downgrade your account right now, your account will get suspended.

I would suggest you to download the uploaded files first. After that, you need to delete the submissions that has the attachments to clear your upload space. When you're done with this, you can go ahead and downgrade your account.

Related guides:
How-to-Download-the-Submission-Files
How-to-Delete-Form-Submission-Data

If you have any questions, let us know. Thank you.