Does this require a lot of gear? Or does it simply act as another gateway?

I tried Kavita but it didn’t have the features I needed. I ended up just throwing them on Nextcloud and using Nextcloud sync onto my reader (Box Air 3c)

At least with my headunit (2015 Toyota). It cannot read the signal messages. Additionally, I remove contact and text permission from Bluetooth to be especially sure.

When you connect to Bluetooth, it asks your phone to share call, contact and SMS information.

Think like the old horrible headunit text implementation, the ability to scan your contact list from the car, and see your recent calls.

Thank goodness for Signal

Yes exactly. The bridge logs into the discord server as a user. Then it mirrors all chats from your user in matrix to the discord.

Oh matrix, every user on the connected server gets a user whose name is their snowflake. Those virtual users post into the matrix server whatever their respective discord users posts.