Will it hurt performance if each view class is moved to a separate .py file?
Here are two points:

1.does it have effect on the performance?

No, or only marginally. Also, It might take some extra time to load all these files into memory (since each file needs to be opened), hence writing these views in individual files indeed might take a few cycles extra. So first of all this is bad idea for increasing performance. 
But that will only happen when you start the webserver. Once the files are loaded, it does not make much difference in what module the view is defined. The interpreter will simply call the function.
That being said, Python is not a language designed to take the absolute most of the CPU anyway. The idea of Python is, to some extent, Programmer convenience over machine performance. Due to Python's very dynamic nature, it will often not result in the fastest programs. The idea is to offer a programmer a convenient environment. Often if you need more processing power, you can buy an extra server, whereas hiring an extra developer is often more costly. Therefore developing a webserver in Django will likely not result in the fastest response times, but it will likely make your job simpler to implement such server.


Django's Architecture


You should also consider Django's architecture. It's a bad exercise to try to change this architecture. In this architecture, everything is designed to avoid duplication(DRY). And if another developer intends to deliver your project, he or she will be able to take it in as little time as possible. As a result, it seems better to keep this architecture and put all your CBVs in one views.py.
I have a Django project with about 100 class-based views (to now) in a views.py file.
Now managing the views is getting harder. If I put each view in a separate .py file and import all in views folder __init__.py, does it affect the performance?
My concern is performance, not code style.
What about DRF class-based views and serializers?