wow thats awesome. I just got an eastern painted yesterday and put her in with my male RES. The RES is always trying to check her out but she sometime snaps at him but they'll be okay i guess.
Yes, the quarantine tank/container would need to be a complete setup as not to hurt the new turtles health. It's necessary to do this to insure the health of both turtles. Sometimes it takes a while for symptoms of illness to present itself in turtles.
That's fine in that occasion. But if you have one healthy turtle and want to introduce a new one into his habitat, it's the safest thing to use the 90 day quarantine system.