Hi, welcome to the forum!
I shall attempt to help you with your questions.
how long to let the water circulate?
Are you referring to cycling a tank? See this article:
Caudata Culture Articles - Cycling
do i need water heater?
It is unlikely, you are more likely to require cooling than heating (depends where you keep the tank and what species you keep), newts and salamanders tend to prefer cooler temperatures than we do.
can i put different types of newts together?
It is inadvisable to mix species.
What kinds of live plants do they like?
Newts and salamanders don't seem to be picky when it comes to fauna, however each species has different requirements, so its more of how many plants? as much as what type of plant?
You may be forced to choose plants that do best in the water temperature you are required to provide. However most plants found at your local fish shop will be fine.
What kind of lighting?
Aquarium lighting is fine, however how often you use it and for how long may be determined by how much natural light your aquarium may get.
I suggest before you proceed any further with your tank design, you have a look through the various care sheets found on Caudata Culture:
Caudata Culture Species Database - All Families and find out what species it is you would like to keep. The tank should really be designed around the species, so when looking for your suitable species, consider what sort of setup you already have, and what temperatures your aquarium is likely to be throughout the year.
