Plenty of people have had cories with eco complete. It is definitely more of a water quality issue.
There are freshwater nerites for sure, but I have never owned them so that research is up to you.
Blue rams are just another name for german blue rams. They are the same thing. Electric blue rams on the other hand are bright blue over their whole body. If you do 2 schools of tetra, my advice is to do rummynose/cardinal with a tetra that compliments their red good like pristella, lemon, or black neon tetra.