Shopify designer

Hi! I have a fairly large project. I'm an agency looking to build some reusable eCommerce Shopify themes for my clients. If I gave you 10-20 websites/products, could you create themes that are ready to go?

Looking for single-product landing pages with quick checkout. Ability to plug in product feed with the "main store." Some pre-installed apps that work well for eCommerce. Most importantly they should be relatively generic, so I should be able to swap in logos, color schemes, products and easily apply the templates for multiple customers. Please let me know if this is something you'd be able to do.