If you are also making a master file with all these GP materials and duplicating GP objects instead of assigning materials to different selections you might be bummed on how cumbersome it is.. object mode, select the object, draw mode. Then back again.
The hotkey alt+Q works the same as with mesh objects, you can move from one object to the next just by hovering over the object you want to work on and hitting alt+Q.
Now, it might be that this workflow is entirely unnecessary with the GP workflow... different layers maybe are smarter? I'm not sure. Very new to it, and used to separating everything into their own objects. But the hotkeys might help someone else..
You don't need a GP object for each material - you just have to store the PNGs or image files as Fake users in the .blend file. You can use the node set up to render out your new materials to an asset library. Using one file you can go back and edit and re-render. I might update the workflow for newer versions. You're right, there might be a better way now!