Does 1 query = 1 visitor to my site?

This will ultimately depend on your integration. A query will simply be used when we receive a valid request, so if your integration is set to send multiple requests for the same visitor (for example, at each page load as they browse through your site), multiple queries would be used for that visitor.

To help keep your query usage in line with your volume of unique site visitors over a given time period, you may wish to explore independently caching query response data in your system for your internal use.