What is the best way to organize work with git and is Ci needed?

Question

git

Hello. I started learning git, there is a very good book , but I have questions about organizing work.
Situation:
I have a "clean" copy of the script that needs to be configured and it will work. I will install and configure it for people. The only question is that there will be 10-15% of code that is unique for each person (its own logic on request), which is written using a set of classes and the classes will be the same everywhere.
What I want, I want the classes from my clean repository to be uploaded to the hosting clients + that the entire project for the client is also stored in some kind of repository, probably it will be a separate repo.
I am using bitbucket. What has come to mind so far is to create a separate repository for each project. Okay, but how then to update only a set of classes (~ 80% of the entire project) to all clients at once?
Perhaps there are some articles on this topic. I also found such a thing as continuous integration, until I realized whether it was necessary specifically in my case or not.

Answer 1

Aren't submodules suitable? The client project will have a submodule of your classes.
Link to docs: git submodules