Good question. At present, we will not shut you off if you exceed the limits of the Starter plan. For metered services (analytics, forms, build minutes et cetera) you will be auto-enrolled on to the Level 1 instance of the service. You will be notified by email before this happens, at regular intervals, as your service usage gets closer to 100%.
It’s also important to note that we will not auto-enrol you back on to Level 0. We assume that your site, enterprise, project or business is going to require the additional usage of our services. However, at the end of your billing cycle and provided that payment has been made made, a button will appear within the UI for the applicable metered service, allowing you to downgrade.
The only exception I can think of is concurrent builds, but the premise for this is the same principle for all tiers: if your current number of builds is equal to your plan’s concurrent build allowance, any later builds will queue up until earlier builds are completed.