How do i store multible objects in an attribute of another class?

iam new to Kotlin and currently working on my first app. Iam using Firebase to create users and log them in and store some data (a link to their profile picture) in a firebase database.

My next step would be to show all registered users in a list and my thought process was, that I need at least two classes to handle this:

Class 1 - RegisteredUser Has a few attributes, such as userId, userName, email and methods like login(), logout() etc. Class 2 - UserManager Holds all objects of the class RegisteredUser and has methods like deleteUser(id), getUserInformation(id), getListOfAllUsers() and so on.

First of all, is this general idea appropriate in android app development or should I choose a completely different approach? (Especially assuming larger user numbers, would there be signifcant performance issues?)

And should be approach be okay, how would I declare these two classes and their attributes/methods?