I like the new river style, simple but good, though it looks a little odd that they have a redder tone than the ocean. Just a matter of taste I guess, but I think it might look more cohesive if they were the same color.
The long river makes me think of the Amazon river, which also goes across almost an entire continent. The whole west coast of South America has a mountain chain along it; something similar on your south coast could help show where all the water for the river comes from, and suggest the long south-to-north slope.
Which geographical features would be more common on higher ground and how climate is affected I'm afraid I'll have to let someone wiser answer!
I haven't had much time to work on this project in the last few months but just wanted to say that I still plan finishing this one day Here's the latest version: