NEVER mix firebelly toads with ANY newts!!!!!!!!!!
Bombina (firebelly toads) are incredibly aggressive feeders and WILL remove legs and tails from your newts. Not to mention the fact that they can tox each other out. Plus, many of the paddle-tailed newts are incredibly aggressive as well and may amputate limbs on the toads.
A simple rule.... NEVER mix amphibian species, especially if you are new to amphibians.
Also, you should never mix animals from different parts of the world.. as each animal carries a load of bacteria and other microbes that their immune systems are used to. When you bring in another animal from another part of the world, they bring their set of microbes with them. The animals will then likely die from this alien bacteria. This is what is known as new world syndrome.. as this is exactly what happened when europeans came over to the americas and wiped out thousands of first nations peoples with a few common european illnesses.
If you want to do a paludarium... Firebelly newts and white-cloud minnows are the ideal choice. Newts always prefer cool temperatures.. and tropical fish aren't comfortable at cooler temps are vice versa. Newts will often succumb to illness if continously kept in the high 70s and low 80s. The bg problem is often people keep newts too warm, or with other species.
So, I seriously hope you consider NOT to mix amphbian species or add any reptiles. You will have the best success if you stick to one species of amphibian and a few fish. Just because pet stores have ridiculous setups like this, does not mean they will work. Remember, pet stores replace dead animals all the time, and also, animals like that are never in those tanks for more than a couple weeks anyway. Sure, the people at the pet store may say a tank like that "works"... but keep in mind that the animals are never there for more than a couple of weeks anyway. People who work at pet stores are often well meaning, but ill informed. I'll dig up a link to species mixing disasters...... but that will be later tonight.
Till then, check out
www.caudata.org and you will find all the info you are looking for.
Good luck