Looking for techniques/advice/discussion

[Billia]

Hello,
This is my first time posting on the forums, despite being a member for quite some time now. The resources available here are incredibly helpful and informative.

I'm finally posting because I've volunteered to make a planetary map for role playing game I'm involved in. I've been working on the map steadily for six months and it's come quite a ways. I joined the role play group and they had already produced a basic map. I took that map and added to it and changed it. But it still doesn't look quite right. I've been trying to create a map that looks similar enough to the original so as not to make the other players of the game redraw their boundaries and re-position their cities and such. But I have been given permission to change some things.

Here is the progression of the map since I've worked on it.
1. http://i.imgur.com/ziDWp09.jpg
2. http://i.imgur.com/BULIvjc.jpg
3. http://i.imgur.com/CkiY82Y.jpg

I'm not very good at making mountains. I'm not the best with textures. And some general tips and advice on how to improve this map would be greatly appreciated.

I work with Gimp, and I have a pretty low-end computer.

Thanks everybody!