Looks pretty nice so far.
Here's my opinions on your specific questions...
- Rivers - Though I only did a quick scan of the map, everything seemed OK - no major 'violations'
- Fonts - My opinion is you try never to use more than 3 different fonts, and you should limit the variations in font size to as few as possible.
- Textures -vs- Symbols - Personally I would stick with one style or the other.
- Oceans/Seas - You could try the wood cut effect many folks use to great effect.