Need Advice - How to implement Custom E-Commerce like Application by taking parts of open source e-commerce projects

Hi everyone.

I’m pretty new to Python and Django coming from a Node.js, Express background. Making the shift to Django because of features like Database ORM, Out of the box Admin panel etc. I am looking to build an e-commerce solution for a customer that works a little like Udemy or Coursera.

I am ready to implement all the custom logic that goes into handling course content, users, API with DRF and all but do not want to reinvent the wheel and implement common E-Commerce functionalities such as Cart, Checkout, Order Handling, Email to Users after order purchase and such things.

How can I achieve a custom Django app from scratch while taking parts of e-commerce functionalities from open source Django e-commerce projects such as Saleor (really like the admin dashboard) or Oscar (heard it has a lot of e-commerce functionalities)?

Note: I do NOT want to start developing my application with those projects as base and start adding my own function or removing parts I do not need. Rather, I want to integrate them into an existing Django application that I develop from scratch.

Has anyone done this or is it better to go with complete custom build? Really want opinion from experienced Django devs. Thanks in advance.