You might get some conflicting advice about using filters with newts. I sure have. In general, I don't usually trust what pet store staff tell me. Some pet stores are great and have knowledgeable salespeople, but many don't.
Based on the books and articles I've read, here's what I've come to understand about the whole filter issue: If you don't use a filter, you will need to change the water more often. Maybe every few days depending on how many animals you have, plants in the tank, how much and what you feed, etc. Filters don't eliminate the need to change the water, but they cut down on the frequency and keep things more stable in between. You still have to test your water, though.
Different types of filters work in different ways--some just grab hold of pieces of "stuff" that's floating around (mechanical filtration), where others also use beneficial bacteria to actually help clear the water of harmful waste breakdown (biological filtration). They also differ in how they are used--Some filters fit inside the tank, some use a tube that inserts into the tank, some go under the gravel.
Larger filters can create some pretty good flow in the tank, with enough current to make it hard for a small newt to swim comfortably, and a really little one could even get stuck by the suction. If you've got a smaller tank, like a 10 gallon, you won't need a very big filter, probably. In my fbn 10 gallon tank, I'm using a Tetra Whisper 10i, which goes in the water. It uses a mesh bag filled with carbon so it's both mechanically and biologically filtering the water. This model is also what I have in my 10 gallon frog/tadpole tank and it does a good job in there. But for the newts?
Right now I'm not sure this filter is the right one to use for them, so I don't suggest running out and getting one. See if anyone else suggests a different model. I'm going to post a question to the group regarding the amount of bubbles that are being produced by this filter.
Your other question, and again, I'm new at amphibians, so this is just my opinion: Tiger salamanders are popular and easy to find. They're terrestrial, not aquatic, though. If you like an aquatic species, and you can provide a cool enough area, consider an axolotyl. They're relatively engaging for this type of animal. If you're going to a reptile show, you will probably see all sorts of choices. It may be a good idea to read up on salamanders in general before you go so you don't end up with an impulse purchase and find out you have something difficult to care for.
Good luck with your search!