Shopify Plugin

We have a tool for Shopify sellers which we have to convert into a Shopify app. Once we did this requirement we have to do the same for BigCommerce too. Please show your past work and experience which help us to take a decision. The tool you have to create is especially for Automotive sellers. Once they install the tool, The tool will ask for a username and password for connecting API, The API is already created so no need for any costing on that.
Once the plugin is installed on the frontend system will ask for the Year|Make|Model|Engine filter. Users can apply filters and see results. See the below sample.
https://partsnation.com/
Please ping me only if you are confident.