3/ I am a huge fan of #Matrix/#Element and even run my own instance. It has huge promise. But it is Not. There. Yet. Some reasons:
#Synapse, the only currently viable Matrix server, is not ready. My Matrix instance hosts ONE person, me. Synapse uses many GB of RAM and 10+GB of disk space, with little tuning for either. It's caused OOMs more than once. And this is AFTER extensive tuning. It cannot be hosted on a Raspberry Pi or even one of the cheaper VPSs.