1. LittleFS. Not the most performant, but the most corruption-resistant, drivers are FOSS, and undemanding of the CPU & OS.
2. I don't encrypt it, that has its own risks. Individual files may be encrypted.
3:
- Photos, in 800x600.
- Boatload of text files - personal, literature, and instructional.
- Key files fot SSH, GnuPG, Bitcoin, Monero and Nostr
- Contacts and bookmarks