Can I import my costs from a spreadsheet?

Ad spend, yes: Settings and then Integrations takes a CSV of dated rows. Product costs come prefilled from Shopify wherever your catalogue carries a unit cost, and are then edited per variant, with each value marked by where it came from: the Shopify prefill, a manual edit or an import.

For a large catalogue with costs living in a spreadsheet, the price list template is the right shape to prepare them in, and support will help you get them in rather than leaving you to type a thousand rows. Rate cards, fees and overhead are entered in their own panels, where the effective dates matter more than the typing.