Is it possible to get an error in our request if we went over a limit?
Yes. Exceeded the quota error message appears.
You need to use a developer key,
For search endpoint is 100 points. Others 1 point. Total of 10000 points for day.
Yes you can get more quota unofficially. For example, these 2 apis of mine:
https://rapidapi.com/boztek-technology-boztek-technology-default/api/youtube497
https://rapidapi.com/boztek-technology-boztek-technology-default/api/youtube-search-download3