Unless he only wants to keep goldfish, I would find a new home for them. The cooler water they require really limits the choices.
For the rest, it depends on a lot (pH, GH, KH). I would most certainly use hardy species, and go really light on the stocking until they get a solid habit of weekly water changes. They'll need a Python or equivalent. Bucket brigade on a 55 gallon every week will be a major deterrent to proper care.
bucket brigade!!! i love that