If you’re already running Pihole, I’d look at other things to do with the Pi.
https://www.adafruit.com/ has a bunch of sensors you can plug into the Pi, python libraries to make them work, and pretty good documentation/examples to get started. If you know a little python, it’s pretty easy to set up a simple web server just to poll those sensors and report their current values. Only slightly more complicated to set up cron jobs to log data to a database and a web page to make graphs.
It’s pretty straightforward to put https://www.home-assistant.io/ in a docker on a Pi. If you have your own local sensors, it will keep track of them, but it can also track data from external sources, like weather & air quality. There a bunch of inexpensive smart plugs ($20-ish) that will let you turn stuff on/off on a schedule or in response to sensor data.
IMO, Pi isn’t great for transport-intensive services like radarr or jellyfin, but, with a Usb HD/SSD might be an option.
Back in the day, I set up a little cluster to run compute jobs. Configured some spare boxes to netboot off the head-node, figured out PBS (dunno what the trendy scheduler is these days), etc. Worked well enough for my use case - a bunch of individually light simulations with a wide array of starting conditions - and I didn’t even have to have HDs for every system.
These days, with some smart switches, you could probably work up a system to power nodes on/off based on the scheduler demand.