Is there a reason you need two containers? Why not just use one very large container? Placing piping between two plastic tubs is going to present sealant challenges. Plastic is flexible and will bow under the weight of water making it tricky to find a water tight solution that will flex with the plastic.
Temperature wise you can either place an aquarium water heater in during the winter or move the whole tub to a frost free area such as an outhouse. It really depends what temperatures you expect and what options you have available. During prolonged sub zero spells a tub of water outside may freeze solid, and no newt can survive that. The container should be frost resistant, UV stable and preferably food grade. Storage tubs made from polyethylene have fairly short lives outdoors as they become brittle. I would be reluctant to use them for aquatic tubs. Rubber would be a safer longterm option.
As for live food, nothing is likely to last long with P.waltl. Some aquatic invertebrates, such as Asellus may survive in small numbers if they have suitable places to hide. Sometimes with large aquatic outdoor enclosures it's hard to keep track of all the inhabitants feeding. I find it's useful to have an area of bare floor where food can be deposited. Newts have a knack of learning where their food is going to be and will congregate there during feeding times. Still, it's a good idea to regularly audit he group for signs that some are not feeding well.