Hi Dim,
Thank you for reaching out. Please find my response to your questions below:
You could log into the Google API console and under your project check the Google Ads API Metrics and monitor the API usage and requests.
You will not get billed based on the access level you have. However, if you hit the limits when making requests with the basic access level, you will not be able to make any more requests during that day.
Thanks and regards,
Xiaoming, Google Ads API Team