I got my Pi4 to be a media player - LibreElec or Kodi - for my old, not-smart TV. It plays my library of CDs&DVDs, frontend for OTA TV, and a variety of streaming services. Fanless, so it doesn’t distract from audio, low power, so I don’t mind leaving it on 24/7. You can configure it to listen to a USB IR receiver, but I control mine from phone via web. The actual media library/NAS and tvheaded run on an old desktop in another room.
My favorite thing is all the sensors you can hook up. Adafruit & Sparkfun have a wide array of sensors with breakout boards for simplicity and well documented python libraries. I started just logging temperature, humidity, then air quality, CO2 to my own database and web page, but eventually expanded to full HomeAssisstant system.
Pihole.






If you want it to be an actual community service, then you want it to be something that outlives your residence, your tenure as event coordinator, and your interest in being the neighborhood IT guy. It’ll be much easier to transfer control of a VPS to your successor than to give them hardware that also hosts a bunch of your personal services.
You can start with a very small, nearly free VPS while you recruit users & scale up as (if) anyone bites. Probably even get the HOA to pay for it.