I don't think that this will work, not in a 3 ft. The CA cross looks like a regular midevil (midas/red devil cross) and they do not play well with others usually. Certainly not in a 3ft tank. I know it seems big now but once those fish start growing it will very small very fast.
Depending on the breed of your pleco, which is likely to be a common or sailfin given that you probably took lfs advice, then that is likely to be really unsuitable for your tank also.