I have grown pothos vines in newt tanks, but you need to be sure that no chemicals have been used on the cuttings prior to putting them in with your animals. Any fertilizers, pesticides, etc, will be very harmful to any newt, let alone new imports (if yours are not captive bred). Even if the cuttings are from plants that you personally do not use chemicals on, I would not use the cuttings if the plant had not been in my possession for many months, as I am sure commercial greenhouses douse their products in plenty of chemicals prior to sell. It just would not be worth the risk.
The pothos did OK for me in low light and low temps while in the newt tank, but never did great. Chinese firebellies really benefit from habitats crammed full of live plants - they like the security that the overgrowth affords them, and the plants aide in achieving good water quality. I have had good luck with elodea, which I have purchased from local Petsmarts. My local store sells them in bunches for pretty inexpensive, and these plants do well in the conditions newts need - cool temps, still water, and relatively low lights. They also can be left free floating and do not need CO2 injection to do well.
Regardless of what plants you decide to use, you will need a light source for them, and get more than what you think you will need - the newts will benefit from all the foliage and I know I have been surprised by how many plants it takes to fill even a 10 gallon aquarium.
Good luck! If you have not already done so, take several hours (days, even) and browse the site - there is so much you can learn and your animals will only benefit from all the knowledge you will have gained
HJ
