Is having two filters a good idea or not?

That’s not crazy at all!
As a general rule of thumb you cant have too much filtration (except perhaps a few specialized cases but I will assume this is just a normal tank..) One thing though, what are you using for filter media? If its just plain old bio media (lava rock, ceramics, floss, etc…) then the more the better…. I personally don’t EVER use any chemical based filter material on ANY of my tanks; but maybe someone on here who does can comment on the question as if you are using some of the stuff from “the dark side” my advice may not be 100% accurate…
And as a point of interest on filters: on my 90 gal; my trusty old Fluval 404 would probably get the job done (can carry probably about 3 or so gals of water.) But I ended up just building my own filter that displaces closer to 40 gals of water AFTER it has been filled with lava rock…
Fish in the wild will have thousands of gals of filtration per fish; in aquariums we super concentrate these little guys, ANYTHING that you can do to polish the water more then the better they are going to be!

Redundancy creates stability.

I reccomend two of everything when it comes to tank equipment. If somethig breaks, it is not an emergency. Additionally with filter doubling up gives you the option of different formats, different media and differant application ideas. It also allows you to change media and clean filters without as much worry of mini-cycles or problems.
Dave

I have at least 2 filters on most of my tanks, and usually each of these filters is designed for a tank twice the size.

On my smaller 10-15 gallon tanks, I generally have one very oversized filter. My newest 10 gallon has an aquaclear designed for up to a 50 gallon. If the flow is too much, you can always turn the flow rate down and still benefit from the increased amount of media in a bigger filter.

i have two 90gph filters on my 20g long tank, because its so long. it helps prevent dead spots.

more filters = more media
more media = more space for beneficial bacteria to grow
more bacteria = less amonia and nitrates

yes 2 filters is a great idea!

absolutely 2 on my tanks.

Look at my sig,n'uff said