That is, indeed, a plenty huge map. If it's going to be packed with information, though, that's just fine. 250 MB isn't too bad for an image this size, if your computer can handle it easily. My last map was about that big, and it had much smaller dimensions than this one.
I like that large river system including the lake in the center part of the continent, and the forest style is a nice change--it's neither symbolic nor an attempt to be photorealistic. It looks painted, which is good.
You need to do some cleanup on your coastlines. There are many places where you have forests growing out of the ocean, which needs to be fixed. I'd magic wand select the ocean, choose the forests layer, and simply delete. That'll do the job of erasing everything that's not over land. Same with the mountains, but you'll probably have to go in and manually clean up some of the symbols that get cut in half that way.
As regards the mountains, since your symbol is transparent, you need to be careful with overlapping them. It just doesn't look quite right to be able to see one mountain through another one.