Tank questions

Is a 90gal tank adequate for 2 common goldfish and a pleco? I'm getting mixed information on google and I want to make sure that will be enough space for the fish before I go out and buy a tank or make and plans.

My current goldfish is only a couple inches long and is in a 36 gallon for the time being. He seems a little like he wants a friend, so I'm thinking about getting him another baby goldfish. But before I do that I need to make plans to upgrade them to a much larger tank in 6 months to a year when they would both be around 4-6inches long.

This might be a terrible idea so I want to run it by you guys before I do anything.