If you take a look at my 45-F journal, you'll see that the 16" Fugeray is really only a 12" light in a 16" body. You'd want the 20" for a 10gal. I cut the light down with a couple layers of fiberglass window screen resting on the glass top of the tank.
Snails do clean up leftovers, usually devour any lost shrimp or young fish before I notice and keep the glass spotless. But the real secret to a clean tank is just keeping feeding in check.
Hey, I loved reading through your tank journal!! Probably especially because it is so similar to what I want to do- a 10 gal tank, low light, planted, with shrimps and cory habrosus.
But, you said that the Finnex 20" is more than low light over a 10 gal tank. After reading the PAR data, I had wondered about that, and was contemplating buying a 16" and modifying the legs somehow to put it over my tank. Do you have any speculation if this would be adequate?
Also, if your light really is too high and you aren't supplementing CO2 - where is your algae? (I'm jealous. I would LOVE for my tank to be that clean. Is the secret the lots of snails? I've never really liked snails all that much)