I've been using a combination of Opentracks for GPS/map and gadgetbridge+PAIesque with an amazfit neo and Decathlon HRM band for metrics and analysis for about a week now, and it's honestly just inferior in every single way compared to my Coros Pace 2.
So there are solutions, but they all kind of suck a little and you have to be willing to accept that.
If streaming in 256kbit/s only required 256kbit/s actual connection, your math is correct...in reality it will need higher bandwidth to stream seamlessly at that bitrate.
Curious, how do you plan to download from your newsgroups if you are not exposed to the internet? This is no different than the internet access e.g. qbit needs.
I've been using freetube for a little over a year, and I have to change something all the time (like every third time i open the app or something) otherwise videos just throw an error and won't load. Same goes for my laptop (also freetube). Newpipe and revanced are even worse for me and some I never got working.
You have to frequently do some shenanigans to get things working because shit keeps breaking. I still do it, but it's honestly annoying AF that i need to tinker with my apps like that all the time.
Hot damn that place is dead...