Good morning!

It's early and I'm just about to finish my first cup of coffee, so whatever I say right now can be affected by morning dumbness, but ... 3 GB per layer? What the heck, lol. That doesn't sound right, to be honest. Maybe the whole project is 3 GB? I usually import textures worth 3-5 mb and that's what I'd consider pretty huge already. 3 GB would be pure madness. I think a project roughly the size of 9000x9500 (that was about the resolution you were working at, right?) with just a few layers (10-20?) can be roundabout 3 GB big, at least that's what GIMP tells you. The actual .xcf-file would probably be about 800mb.

Anyway, the texture blending of the grassy areas looks good, the transition from grassy to stone seems a bit abrupt, though. If you're working with a layer mask (and I know there's nothing you love more than layer masks ), you can select the mask and apply a gaussian blur to make it blend more seamlessly. Or you can use the smudge tool and "blur" the transitions by hand, which allows for more freedom. The stone texture looks like it's set to overlay, by the way, which kind of corrupts your line work. If the line work is on a separate layer with an alpha channel (meaning the layer consists only of the line work and nothing else), you can move the layer above the overlay layer and it should be solid black again.