Corys and khulis wont actually clean up the mess though they will just turn the sand making it more likely you have rotting matter in your substrate affecting water quality. MTS will sift the sand and eat the fish waste as well as any excess food. By all means get khuli loaches as well but they won't do much for your cleanliness.
I have just moved my betta over to an 8 gallon tank the stocking will be - 3 striped khuli loaches + 1 black khuli loach, CT male betta, 4 african dwarf frogs, 60 cherry shrimp, 2 horned nerites, 3 apple snails at a relatively small size and Malaysian trumpet snails. Ramshorns and pond snails have already managed to transfer from my other tank as well as 2 of my guppy fry. My filtration is really excessive in this tank though hence the very very high stocking levels, I have heavily planted both tanks, 2 fluval1+, interpet pf1, diy filter (equivalent sponge area to 9.7 x a single fluval 1+) the filtration connects the 8 gallon and 5 gallon together. The 5 gallon contains 2 black corys, 2 albino corys, 2 male endlers, 3 guppy females, the fry, all previously mentioned snails, assassin snails, cherry shrimp, tiger shrimp, amano shrimp, black shrimp and blue tiger shrimp. Eventually I plan to connect the 2 tanks with a fish tube but atm bit worried the assassins will eat my apple snails and unsure whether I actually want them freely moving between the tanks.