Well, Blender’s texpainting is serviceable, but better-suited for base coats and roughwork up to medium detail. The approach you took of doing the finer detail in dedicated software seems to be the best way to go for that, while doing the roughwork in Blender will allow you to paint directly on the model and see your changes in realtime (which would save you all of those import/export cycles).
There is a dedicated Texture Painting course that will cover the basics; however, based on the project you’ve completed here, I don’t think it will show you anything more than a few tips and tricks to do things faster. Worth checking out if you’d like a better idea of what Blender can handle on its own for texpainting.