Custom Classes : general questions

Hello,

1 - What do you think about creating a class that I can use in many Models, Views and Controllers ? 
2 - Where should I put this class "for a good practice" and call it if I would like to use it with several controllers, models and views ? 
3 - And last question : Does something already exists like that ? ... A plugin in CodeIgniter4 for adding quickly content in databases ?

Thank you a lot for your help !

The class already exists and it bears the name of the framework - CodeIgniter.