you can keep a full grown one in a 125g, it will grow to allitle over a foot, as far as tank mates realitvly pasive fish that are big enough not to be eaten, in my opinion go w/ gars or other big fish like cichlids, big cats.
good for cleaning the bottom of the tank left over foods. Dont eat nothing that dont fit in its mouth. cooler then a pleco. as mentioned above the sizes of them.