The latest version of HA has simplified automatic backups so you don't need proxmox for that anymore as of a few months ago. The whole thing has come a long way since I started using it in 2019 or so. It'll run on a pi 4 just fine, but when you start adding things like Z2M and Frigate or ESPHome, you'll wish you had the overhead for those. I would say get an old SFF or USFF PC with an i5 of at least a 6th gen. Add 16-32gb of ram and get rolling for well less than the price of a pi. That 6th gen or higher is just in case you want to process video on it at some point because that's when quicksync or whatever they called it became part of the intel chips.
Then go to chatgpt and ask it to create some dashboards for you based on the things you want to be able to see. Choose your favorites and ask for help implementing. The AI tools have gotten pretty good, even to the point of being able to do interactive floorplans for you.