A 1000 items list is about ~65kB (64 bytes + 1 byte separator), let's double it for the encryption layers and sum up to 150kB adding some other config data.

With 124GB we accommodate 1M users, that pessimistically could read+write 1-2 times a day to do automatic backups; 2M operations are 22req/sec (11 read + 11 write), perhaps doable on a low/middle range VPS that can survive by anonymous donations.