Thanks all!

It shouldn't be difficult to clean. The soil is bioactive anyway and the rest is just spot cleaning any lumps of poop and wiping down the glass when it gets water spots.

I created the rivers with the hydroton pellets. I put down a layer, about 1.5", of pellets, and then cleared an area with my hands to "carve" out the river. I used large rocks to keep the river clear while I put down a layer of plastic screen, then I put the rocks ON the screen which held the screen down in the river section. Once I put down aquarium gravel in the river and put the dirt on top of the screen everywhere else, everything stayed in place.

I can still seem some screen on the banks of the river - I am going to get some aquarium mosses which should grow over that nicely.