I usually do the 'cluster of three lines' and 'cluster of 7 lines' to make little grass clumps for wetlands!

I will note you can always draw patches over top of a map even if you don't have the layers. In fact, even with the layers, patching in a river instead of editing the old rivers is often an easier way to go about it. That said, for rivers I'd be willing to provide the layer as an independent png. And I provide future edits when requested for low fees, most of us do, even if I really wish some of my clients who come back for edits would just let me redo all of the work LOL

And yeah, the Cintiq / screen tablet does make all the difference. I hate to say it but my work exponentially improved once I got a larger screen tablet. Though I do miss having a small tablet for using as a replacement mouse. If you do artwork commissions you'll probably love to have one, heh. But do consider low cost alternatives, I have heard they've come a long way. I do see how you could be conflicted if your career keeps you pretty busy and makes you decent money; that is a good recipe to commission an artist instead.