Not to bad so far...
1) The darker water isn't that bad - but if your not happy with it then change it.
2) Some weird stuff going on in your lakes
3) I like the hills/mountains but they have a little to much white in them I think.
4) Your 'roughed in' rivers don't seem to be breaking any rules
To add a pattern in photoshop is easy...
1) Open the pattern/texture file you want to add
2) Click EDIT > DEFINE PATTERN
3) Give a name to the pattern and click OK
This will add it to the current pattern 'group'