I was mainly interested in the chassis, and put my gear in it. When I seen the price, I was less excited.

DIY, only regret was the case I used. Silverstone CS351. Just don't. Its a massive pain to work in, and getting to the lower internal two HDD bays requires tearing the whole thing apart. I picked it because it would hold everything I was using without mods. Its just a pain to work on.

WAN IP is no longer the same

Then you do not have a static IP and this will happen again.

You need to get something setup that will update your DNS records with your register when your IP changes. I use cloudflare for mine like this vid https://www.youtube.com/watch?v=Nf7m3h11y-s

or, pony up with your ISP for a static IP.

What Eaton unit are you using?

I run hand full of Eaton 5P 750va in satellite network racks in the building. Those are good to 600w power delivery. No issues with them.

Put a meter like a Kill-a-Watt on that system and watch the power draw on start up. Might be worth hooking up another system to it as well and see if the problem persists. If it doesn't act up on the 2nd system, might be an issue with the PSUs for the 1st system and what killed the APC.

are you running 9" displays in place of physical photos in frames? Curious how this is setup. Is there a write-up somewhere?

edit: same for "the wall" with the 6x 55" screens.