How to determine how much did I burn through my AWS API gateway plan and how to put a cap on billing?

Question

I've set up an AWS HTTP API gateway, a reverse proxy to my service running on Heroku:

• 1x API gateway
• 1x Route
• 1x Integration
• 1x Custom domain with an SSL certificate

This is all working fine right now.

Although I've spent days studying AWS, two questions still remained unanswered to me:

1. How do I know how much did I burn through my free tier (or any other tier) on AWS?
2. How can I put a cap on API requests/costs so that if I misconfigure something or if somebody attacks my web site, I won't end up paying $$$ in AWS fees?

Thanks!