That sounds like a pretty heavy load (at least if they are all full grown it would be) I would keep the tetra and add the 405.
I am using the fluval 405 on my 90 gallon and it is great but it is a planted tank with a low bioload and weekly water changes.
I agree that the ugf
can be quite noisy. And using a canister will be a big difference in the noise level but I would place the return from the new fluval in such a way that it still disturbs the surface so you get adequate oxygen exchange.
If you keep the existing tetra filter you might be able to add the new filter without much of a mini cycle.
Hope that helps.