Before you go for a custom e-commerce solution I would recommend please take a look at ready-made solutions like Magneto, shopify, zepo etc.
- For custom e-commerce solution I would recommend open source e-commerce framework like Magneto, prestashop.
- For android application the solution would depend on the extent of native experience, but for most usage a hybrid application using React / Angular (ionic) is what is recommended. With PWA you can event have an existing responsive website as an application which would save you a lot development cost.
- Ensure response design which will allow users to seamlessly use the website in difference devices and get better google ranking.
- If you build the front-end with Angular it would make it easy to convert it to an android application with https://ionicframework.com/.