What sort of classes do you mean? Views? Models? Other? For us it hasn't changed much. Our apps were pretty self-contained so that splitting them into separate services isn't very arduous.

Stuff that is shared between apps is often related to 3rd party integrations, which could be moved into a separate (often asynchronous) worker/ service. In reality most of these design choices are done on a case by case basis, based on time/ cost/ maintenance.

Yeah my main concern is for models. I can see it helps if you have distinct django apps already, in my case I have one main monolithic app. As an example I use elasticsearch, but I post process the results using models. ES is a service already do I really want to iolate some logic and build another service on top of that?

We extracted common code in a library, which we reuse in each microservice.