If you're using other artists' work without permission, there's a real risk of copyright issues, especially if you're charging for it. I'd recommend creating original art or getting permission before building a Patreon around it.
From what I've seen, later editions usually don't change the sculpt itself, but the paintwork can be refined a bit. Colors may look brighter or more balanced, and small details like shading or finish can improve. The main difference tends to be in the overall polish rather than the design.