Readarr sucks (not due to being a bad software... Don't get me wrong). Maybe due to how the media itself is messy, no good source like IMDb, messy releases that are hard to decypher.... Even worse for non English languages, let me tell you.
Also, cannot manage ebook+audiobook and you need two instances for just that.
I gave up using it as well.
Calibre seems better to manage, and to search&download you can always use prowlarr directly.
You don't. Providing you have an upstream gateway that do the firewall for you, provided you don't have an open WiFi, provided you use a reverse proxy, provided you have sane network settings all around, provided you run linux(or similar).
Even better if you are behind CGNAT.
Provided you know what you are doing.
On the other hand, setting up a firewall in a safe way is no easy task either.
I use an opnSense on top of my home network, given all the above "provided".
Before that, I never run a firewall and never had an issue. Always being cg-nat tough.
That connection I expect to be secured by using signature keys that are private and would need to be released by Tesla to allow anybody connect its car to a different back end.
Link doesn't seems to point to a product