Looking for feedback on growth metrics

Hello,

I'm building a tool, Daylitics, to help small ecomm shops and startups reach their target customers more effectively. It combines Shopify sales data with data from the major social/ad platforms (Google, Facebook, and Instagram) to provide insights into the most profitable channels, campaigns, and content.

I'm looking for feedback on what metrics are used to steer decision making for small businesses using paid acquisition channels. For instance, is it ROAS (return on ad spend), total sales, total spend, conversion, all of the above, or something else?

Additionally, I would be interested in learning more on how you handle discrepancies on metrics across the various channels. For instance, what if Google Analytics is showing a different sales amount than Shopify?

Thanks for your help!