Hi oosie,
Welcome to the forum, I don't think I've said hello yet!
Given that the artwork is entirely compatible, I don't see any issues with what you've suggested, all the tiles can be mixed it. I suspect you will have some issues playing with both Rivers, because it will create a very long river. The issue will be the same as those who play with the River, River 2 and any mix of River tiles. What you propose can't be too terrible; but you may end up with an enormous farm.