The problem with the send to Kindle option is email attachment size limit. For books it’s fine but manga and comics are usually too big.
My Kindle is old enough that I was able to jailbreak it and install KOReader so I can just download from my Calibre server directly via OPDS. Otherwise if it’s too big for email you’ll have to do it over USB I think.
Jellyseerr is about to add Postgres support which is sweet if you run in any kind of cluster configuration like kubernetes.