Ah, thank you guys! I really appreciate the feedback :]

I'm going to look at more maps to get a better idea of how the coastlines should look--at the moment they are too straight, but I just wanted to have a general idea of what it'd look like. Now I can sketch over what I have and see what I get.

Islands are definitely a thing I plan on adding. Right now, I was only focusing on getting the main continents done. After that comes the islands, I think. As far as size goes, I'm not sure how big I'll keep things. I've just been working on 16k by 16k at 300 dpi--though I haven't thought much about scaling yet. I probably should.

Also, thank you for the feedback on the rivers--I was unsure of if they'd look realistic as is. I'll straighten them out and hopefully they'll look more believable.