I had a common pleco (hypostomus) That I kept in with a couple of blue gill, green sunfish, staghorn sculpin, yellow fin goby, and a group of smaller bull head catfish. Generally speaking spats were rare, the pleco received almost no attention. Although he spent most of the day in his cave and everyone had available hiding place. However he was probably the longest guy in the tank (some others were bigger) everyone else was around 10cm, he was closer 12-14.
Second question: I ran the tank around 20-21 degrees. cooler than tropical, but only a few degrees. Pleco, might have been slower, less active, but not sickly or distressed. He always served his purpose and kept the glass algae free.
This was only my observation. I hope it helps.