If you're feeling adventurous, you could cut your front panel audio wires and connect them to a new 3.5mm jack inside the case. It might be a lil janky but it would get the job done for <$10
AudioQuest Dragonfly wouldn't be a bad way to go. I have a Red on my PC because the onboard mobo audio picks up USB noise. I've also got a Cobalt for my phone/headphones. They have a firmware update utility for the Red/Black that you manually install and can uninstall afterwards, the Cobalt ships with current FW and hasn't been updated yet. That said, they're pretty expensive for what they are and I got both of mine 50+% off. If you're considering a "proper" audio setup, I'd go straight to to the Denon unit you're looking at
Listen to this guy. Most LED tape is 12V or 24V. A 5V 20A power supply may meet your wattage requirement, but the LED tape will need it at 12V to function properly.
If you have a local audio/video company, give them a call. Most of the big brands have a whole product line geared towards hospitality use that gives much greater control over "smart" features. They're usually not available to the general public, but an A/V dealer should be able to hook you up
If it's cable internet and not fiber/DSL, I'd look at connecting the ISP's coax to the house's coax. Provided all of the house's coax ports are connected to a splitter, you could feed the ISP coax into the nearest port and plug the cable modem into the office port.
I was originally going to host my instance on my own hardware but decided to use a $6/mo droplet on DigitalOcean. Seems to work well enough for me and my LCS bot. Picked up a domain off Google Domains for $20/year or so. It's been a fun project and I've learned a lot along the way.
Really shouldn't be hard to figure out given the events of the past few days...