No corydoras. A lot of goldfish grow too big and are capable of swallowing cories easily. Once this happens, there will come a time you will choose which of the fish to save. Saving both is almost impossible especially if the catfish's spines get lodged between the jaws.
As far as plecos are concerned, not all plecos behave similarly. Bristlenose plecos in general are quite acceptable as tankmates for goldfish. Of course, it totally depends how they behave towards their tankmates. There are exceptions. Male bristlenoses tend to be territorial but may learn to coexist well with goldfish especially when wellfed. I've successfully kept BN plecos with goldies with no issues however but that could only owe to the fact I kept mostly females. Don't even attempt whiptail plecos. They're too slender and fit almost perfectly in your goldfish's gaping mouths.
Regarding the issue of goldfish being tropical, I don't think so. They do have tolerance for higher temperature but on some extent, this will have dire effects to the fish. Goldfish are heavy oxygen consumers so warm temperature won't exactly fit right to them unless well aerated. Fancies in particular are best kept at an ideal temperature range of 72-78 degrees Fahrenheit. Singletails (with the inclusion of watonais, wakins and jikins-doubletails) are more tolerant to cooler waters.