Cories do a good job at keeping the bottom of the tank clean. I have Cories in 3 of my tanks. When I feed my fish if any falls to the gravel, they eats it. I also give them shrimp pellets to make sure that they are getting enough food. Just don't overfeed. They eat the left-over food, not fish poop. So you will still have to vaccum your gravel.
I like your fish selection. They gives me some ideas for my 20 gallon that I will have empty as soon as my 125 gallon gets set up and cycled.