FW clams are filter feeders. They require a well-aged, very heavily planted tank with just tons of "stuff" in the water column and very good water circulation. And even with all of that, you hear a lot more failure stories than success stories in keeping them alive for any length of time. They also need a pretty fine sand substrate so they can bury themselves down in the sand. There would be no impact on pH unless the clam died and you left the shell in the tank for a long time after the clam's death.
There would be no conflicts with your other tank occupants, other than the warnings you've been given already that you are going to run out of room in your 10 gallon tank with your current stocking plans. 10 gallon tanks seem big at first but once you start accounting for the sizes of grown fish, you discover pretty quickly they aren't that big at all. Zebra danios are such active, fast swimmers I personally think they need a tank larger than 10 gallons. My advice would be to take back the danio, and make the focus on this tank being a guppy tank. They would be your fish for the main water column, and then you could get maybe 4 corys for the bottom (6 if you can find pygmy corys or some other "dwarf" variety of cory). Between the corys and the guppies, that would probaby max out your bioload. If you really wanted something "different" for the tank as well, you could add a few dwarf shrimp (ghost shrimp can be found in most stores, or if you have a really good aquarium store near you, you might be able to find red cherry shrimp). Shrimps would give you something unusual and fun for the tank, without adding to your bioload. Adults would be safe with the fish you have, though babies would of course be eaten almost immediately.
Oh, also, I am assuming your tank is already completely cycled? If not, add *nothing* new to this tank until the cycle is complete.
