Im sorry to say it but your tank is very overstocked. 1 single goldfish would be enough for a 60 litre but even that would be pushing it. 4 goldfish would need a tank well over triple the size, and then a plec aswell?
i would advise either getting a larger tank or rehoming these fish and getting ones more suitable to your tank size.
Goldfish produce an awful lot of waste, which in turn produces ammonia. If you dont know about the nitrogen cycle then i'd advise reading up on it asap.
If your plec is anything other than a dwarf species (like a bristlenose) then it will grow to over a foot long. They also produce huge amounts of waste requiring a big tank.
Also, lots of goldfish prefer cooler water and im not sure if the plec would be too happy. Sorry to sound negative!
In the right tank environment these fish should last 10 years and more. They will also all get very big. The 'fish grow to the size of their tank' is a myth. Whilst their body growth will be stunted, their internals will keep growing and they will live a very unhappy life and die early.
Find out your water parameters (pH and hardness) and then people on here will be able to help with stocking