

I believe i can self-host a matrix client but no idea how well it will work with people currently having notifications by discord bot on their phone
In my opinion discord is not yet enshittified enough for these problems to be easily solved. Give it a couple more years, if matrix gains just a bit more traction, the scaffolding to do stuff like that will be worked out.
It’s much higher than zero, if let’s say your ssd goes kaput & you try moving everything at once to a new one. That action by itself comes with risk, especially if the usb stick is very large & manufactured after covid. There is also the bit rot issue, usb sticks are useless as backup solutions for any use case, it’s just a false sense of security.