Need your advice. Plugin, module or static library?

I don’t know what is the best solution for my problematic.

I’ve developped a game with a dedicated server. During the development, I’ve created several classes : Dialog, tooltip, edit, … for Slate.
Now, I’m starting the development of a game launcher. I would like to reuse the classes I’ve developped. The majority of classes are derived from UE4 classes.

The worst, for me, will be to copy the classes from the game project to the launcher project.

What is the best solution ?
Developping a plug-in, module or put the classes in a library ? For static library I’m not sure we can do it if the classes derived from UE4 classes.

Anyone has suggestions ?
Txs for your help.
D.