Share the best tips for a Productized Service

Hello I had this Idea to build a a Service like PSDtohtml but with webflow.
For example you are having a landingpage in sketch and I will bring it to webflow. And then you can choose to use the CMS or you get exportedcode.

What is the best way to test this kind of business and how to find out what prices Designers or agency will pay?

How to create packages that people will buy?

Any Ideas on how to start this journey?

Best wishes Chris