I would clarify/recommend not being an exit relay, just a middle relay. Back in the days before HTTPS was widely used I ran an Tor exit relay. I then found in my firewall logs all the URL’s and user/pass. I could see where everyone was going. I started “investigating” what people were using the Tor for. This lasted around 5 mins as after a few normal sites visited the logs were full of the Internet’s most unsavory content and very illegal… and all exiting from my home IP… I never had a knock at my door thankfully as I would of had some explaining to do 
I moved on to being middle relay.
I have not run any relays now for years but I still donate to Tor as I think is a valuable service for good overall.
I do have a Pi running a Tor hidden service (Dark website) I am experimenting with this on and off atm with the idea of running my existing Pi 4 8gb Nextcloud installation as a hidden service. Not that it needs to be hidden but atm I have a domain name but the registrar has control over this. As a hidden service I would be in control of the server address or at least more control. Pi 4 8gb is great! I like having 7gb of ram free!
There is a TWIT thread of peoples uses for Pi here: Rapsberry Pi - What’s your usage?
mine atm.
Pi 3 - email server
Pi 3 - Pi-hole
Pi 4 - Nextcloud
Pi 3 - Tor hidden service
Pi ? - Remote central heating control - future project - I have the relays etc just need to get round to putting together.
Pi ? - 3d Printer controller for my 3d printer - future project
Pi 3 - RetroPi gaming retired
I also like the idea of a video doorbell. I purchased the camera module a while back but have not even opened the box yet… So many things to do with a Pi so little time.