Each database (MySQL, Postgres, SQL Server etc.), each Data warehouse (Snowflake, Redshift etc.) as well as each SaaS business application (Salesforce, Jira, Hubspot, ERP, CRM, Accounting etc.) that you connect is counted as one data connection towards your license limit. If you connect for example two Hubspot accounts, this will count as two connections.
The built-in data warehouse is included in the license and does not count as a database towards your license limit.
Each pipeline for a SaaS connection will create a schema in your DWH (not a separate DB) and it will create tables for each object type (customers, invoices, tasks, products, transactions etc). Most SaaS connections will create between 10 and 100 tables, you can choose which tables to sync and which should be excluded.