Got a big collection of magazines or games/software that you can easily preserve?
Here are a couple of places you can check to see if anything is in need.
CPC-Power is largely in French, but it is likely the most complete collection of Amstrad software out there, but even then, there’s plenty that’s un-dumped or scanned. They have a complete list in their “need help” section, linked above.
https://acpc.me
ACME keeps “stub” files of each missing file, and has a system of being able to see at a glance if an issue is missing, by way of a small low battery icon. It takes a bit of searching, but it’s easy to navigate.
For scanning: I recommend for fanzines 600dpi in greyscale, for best quality of scan.
For Cassette dumps: Get a good cassette deck wired up to your PC, record in Mono, and save as a WAV file. No compression of any sort is important.