I like your plan, lot's of room to "play" for the frogs, and some water. With lot's of plants in the background many species will feel at home in this tank!

Personally I wouldn't make such a big ledge, I would use some big branches to make a more natural ledge. But that's just my personal taste.
Instead of rocks you could use styrofoam to create fake rocks (less weight on the glass). I like the idea of the river. Are you using pvc for easy cleaning?
You have thought carefully about placing a fan, and other devices such as lights and the fogger. I don't think there are any mistakes in your plan.

Keep us posted during the build of this tank, lot's of people like to read this type of threads (including me!)

Have fun building this tank!