I have an M3 iMac with 16/512 and I'm very happy with it. Yes, the 4.5K display is very nice. I also appreciate the 6-speaker sound system. My one small quibble is that I wish they would have put the Apple logo on the chin like the previous iMacs, but it's certainly not a deal breaker. I have the Apple Magic Keyboard with numeric keypad and Apple Magic Mouse which I've been content with for years. I actually have two Magic Mice (one from my previous iMac) so if one needs charging I have the other to use if I need it.
I use my iMac primarily for my hobby of 3D modelling and I'm quite pleased with its performance. And I got my M3 from Apple's certified refurb store. Two years on now and no issues.
The only aftermarket accessories I got for it were a Minisopuru pedestal dock and a 2TB Samsung 990 Pro M.2 drive (that fits inside the dock). Nice little setup and I don't have to reach around back to plug anything into the iMac. The dock has USB-C, USB-A, HDMI, standard and micro SD card slots.