Quite a rabbit hole but you can look at bazarr which can be integrated with radarr (movies), sonarr (tv).But Kodi also has a facility to download subs on the fly, as long as you set the sources.
You have to serve the media. It's not going on the firestick directly but you'll either need a server backhand like jellyfin, or just set up an smb fileshare on your computer with all the media and point kodi at it.
The host isn't really the issue. It's the container. How do I access the container with a name rather than number.
I've previously had issues with timezones, and yours are all over the shop.