Hi, we customized lite chekout many times.
For example https://limonad.ua/ desktop and mobile.
https://legrand-collection.com.ua/ here more easy variant.
"Down side is that in every update that revises the lite checkout files you have to update the code again" - better change code files, not overrided by hooks. When you will upgrade need compare changed files and redo changes, if what will do, who done this changes it will be very fast. If you need any changes and you have understanding and algorithm we can help you.