

[…] I’d like to be able to backup to my home server. The main thing would probably just be my photos […]
For the photos, since you have a home server, have you heard of Immich? For anything else, there was a time when I could have recommended syncthing-android, but development on that has been discontinued, though you can still try using it. Some privacy-conscious cloud services may allow you to sync app folders, backing up WhatsApp that way, but I have no experience with that.
is the 8a likely to drop much in price after that? I don’t know how quickly the prices drop but considering the 8a is currently £500 I can’t see it dropping to <£300
Instead of buying straight from Google, you can consider buying a refurbished 8a off ebay or something local - my last two Pixel purchases have been through that method. It tends to be substantially cheaper than buying new, even as little as 6 months after the product launch, and the 8a launched 9 months ago. Just be cautious of seller ratings, reputations, and consistency - prices are lower there because it’s more of a risk for the buyer.
Download all the music you like, whether buying it on Bandcamp or Amazon or pirating it for literally any reason. If it’s too much media to keep locally on your phone then host it on a computer in your house with one of any number of hosting solutions (Jellyfin, Plex, Subsonic, etc.) and VPN your phone’s internet connection to your home network so you can stream them from anywhere without having to set up and secure another method of remotely streaming it. If you were on Android I’d recommend Symfonium, but I don’t know anything about the iOS app ecosystem.