Do I really need it, or is it a luxury?

2D and side imaging is what I use the most. Never use the down.

Down imaging is great for telling what size of bait your throwing on. Side imaging is great for shallow water

Im rigging up my first boat, and BP is running a deal on the Lowrance Elite5. Free install, 3 year Warranty for $$500, holy [censored] this stuff is expensive

Mapping and had color sonar is the most important. IMO

You'll use 2D and SI more than anything for catfish but DI and SI come hand in hand.

If you're not going all in then paying extra for DI is a waste of money.

Can yall give me some advice on what unit?

You do not need any of that to be a successful fisherman. Having a unit for safety meaning be able to tell depth and having GPS for those unexpected foul weather events is the most important. I see more and more folks staring at those screens and relying upon them. Call me old fashioned, but seems the reward is diminished a bit. I am not against all advancements in the industry, but I fear they are taking it too far.

I can tell you that I started with a cheap black and white unit. Couldn't see it in most light, so it wasn't very helpful. Finally upgraded to one with GPS and that was worth the money. Next unit had color and that was also worth the money. I would recommend one with color and GPS. Inhale an elite 7 and that gives a good screen size, but a necessity.

How much do you want to spend?

Around the 500 mark

You can get a Lowrance HDS 5 for that much. That is a great unit that I have on the front of my boat. If you can scrape together a little bit more, you can get the Elite 7 HDI and have down imaging as well. Try to find last years or reconditioned units and you can save about $100. Then when you are ready to spend that much again, you can upgrade to side imaging. I'm afraid I have zero knowledge about Hummingbird units, but I'm sure somebody else will post that pretty quick.

I personally use Humminbird. Started with the 997 and switched to 1197 a few years ago and still use the same unit. The bigger screen makes all the difference when SI. My opinion. Lowrance is making excellent units also.

I agree with Simpson....at least for catfish. The sonar tools are great for crappie fishing but I only need to know depth for catching cats.

My two cents , I just bought a used 997 hummingbird about two months ago, I guide and caught plenty of fish before I had the unit. But I love it ! I use the SI all the time, I fish the same spots I've fished for years but now I can pull into a cove make one pass and see fish in the cove, helps me eliminate water faster rather than the old method of 30 minutes in one spot no bites move to the next. That's just my opinion