Wow that sounds like quite a plant! Christmas cactus likes moderate temperatures and bright but indirect light. Keep the soil moist but not soggy you can allow it to go through a semi drought period in late summer prior to resuming fall watering and feeding if you like but don't let it get too dry for too long.
The plastic pot is fine if you don't over water. The new light polymer pots are also fine. Take care when you attempt to repot it and enlist a couple of additional sets of hands as it will be rather brittle. It is good that you are rooting cuttings just in case. Its very size and weight are leading to potential problems for the plant. Good luck and what a wonderful plant!
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