The first sync will be the most calls used and it's dependent on the number of records. It's still unlikely to reach your limit.
We make use of SFDC's Streaming API to identify new and updated records.
- Every time a lead or account record is created we make an API request to enrich it.
- Every time a lead/account record's Website or Email is updated we issue another API request to enrich it.
We also poll your org for missing enrichments every 30 minutes. Depending on how many missing enrichments there is, we may use the REST API or the Bulk API to save you some requests.