How many listing you can create under one Google account? What's the maximum limit?

From what I understand, there is no limit right now.

• If your profiles were created before October 2017: You can own up to a maximum of 100 business profiles, including Google+ brand pages and YouTube channels.
• If your profiles were created on or after October 2017: You can own any number of business profiles.

https://support.google.com/business/answer/3452778?hl=en

There is no limit for creating the business profiles as one can create 100 or more than 100 but the excess of anything is not good. So creating 100 to 150 will be a good decision.