I don't see any problems with the size off tank you wanna build for your oscars ! but how many oscars are you putting in it ? Oh 2 oscars just read your sig. well 360 gal is more than enough room fro all those fish in your 55gal you could even pop some more oscars in there ! and glass thickness i should imagin 20mm to 25mm. On my 180 gal it's 15mm thick so more water more glass more thickness !