Rubbernoses are compatiable with goldfish.
Any time you buy a new fish you always want to float him also ask the fish store what the Ph is so that you can float longer and add some water from your tank to his bag slowly for 10 mins before you add him to the tank plecos of this kind can die very easily from ph shock.
As for the living conditions they like hiding spots like plants and such.
Food they will eat what ever the goldfish eat and will eat brown algae and some green but not the hard green algae.
They get up to 4-5" long and will hide out most of the day and come out at night