Hey Jazz,
as far as I know there isn’t limitation of the number of data sources you can use as connectors. However every source could have limitations of the volume of data you can fetch. For example MySQL connector has 150k rows limits: https://support.google.com/looker-studio/answer/7088031
You can read more details for any data source by Learn more links:
Hope it does help,
Kind regards,
Krassi