In order to organize usage of my sites through the dashboard on the google cloud platform I would like to assign individual api keys, one per site. I know that a billing account has a limit of 5 projects, but can a project have any number of keys?
I'm using hundreds of keys now. This seems a project can have unlimited number of keys.
Only the queries per second (QPS) is limited by API: https://developers.google.com/maps/faq#usage_apis
Number of queries per day is not limited, it's just your billing.