I received a 55 gallon tank and stand from a family member. She had very recently lost her goldfish to Ich, in this tank. The filters included with it are dinosaurs (not longer produced), so I tossed those out, so all I have is the tank, lights and stand. How do I go about sterilizing the inside of the tank without having to put it outside?

(I have an AC 110 and AC 70 on its way for new filtration, and will be using cycled media to get it going). My biggest concern is the fact I will be using my cycled media and the last thing I want to do is have to medicate a tank and lose all of bb in my media and have to start over.
Also, I have heard both yes and no answers to this question, but I would like to get more insight... I know that it is said the GSP's need 30 gallons per fish. Would it be wise to house two together in my 55? If not, I plan on getting a couple Figure 8's, they're just harder to come by.
Thanks for reading, and for your advice!