matrix What other cheap storage providers are out there?
We use: https://servarica.com/hybrid-kvm-plans/ in Montreal, Canada.
matrix What filesystem is better to use anyway? Still BRTfs or EXT4?
It's up for debate, some people reporting performance issues with BTRFS, while EXT4 misses many features due to being old.
BTRFS created with --csum xxhash can run the checksumming up to 50% faster, depending on hardware. Mounting with noatime (plenty of online sources for this) and compress=zstd:1 (less reading and writing, more CPU use -> great on slow HDD) can make further big performance improvements. Whatever proper linux filesystem you choose will work though, as long as it's not something crazy like NFS/Samba/FTP/PigeonFS or whatever some people built to use disks far removed from their server.