Hi July, welcome to the guild!

One thing I had to get used to doing on digital maps, even when I was coloring a photograph of a physical map, was adding a background paper or canvas texture. That would really help blend things together; otherwise I think purely digital maps end up looking like there's artificially blank space separating different elements. The right texture could also enhance the "mistakes" you injected, more than varying opacity on brushes does. I'd suggest experimenting a little with different texture images and different layer blending styles on them.