Best Practices for Using Storeleads with Clay for E-commerce Data

Hi All! Looking for some advice from any Clay users who have used Storeleads before. Currently trying to target Shopify + Magento stores. We've had a VA scraping the data from Storeleads which just doesn't scale. What's the best way to use Storeleads with Clay? Is it better to export from Storeleads and import to Clay via CSV as this seems cheaper than using the Clay API to import? What are the maximum rows you can import into Clay as there is around 160k Shopify stores in the UK which I could potentially import and then filter based on ICP and messaging