Open registration if and only if you are ready for routine maintenance, creating cleaning schedules, applying spam filters, balancing resource usage, etc. Not to discourage, but for you to know what you really want. If server is for friends and family, just leave registration closed.

My recommendation, as someone hosting a public server is to first host the server for yourself, play for some time, join some rooms on other servers, then invite friends, then if you feel ready and willing open it to the public.

Matrix Authentication Service is good to have, as you can use next-gen Element X which is most polished app as for now.

At least one. Just one actively manufactured phone with full hardware support 🙏

Requiring Google Play and Google account to download and is proprietary, I’ll pass.

Spyware can alter the database of accessed files.

Spreadsheet

Using it on all my devices. It’s there, globally and working. What feels constantly away is getting rid of IPv4.

Don’t you have 5€/mo even? Because that what Hetzner VPS costs. Or a little spare for used Raspberry Pi 4?

Maybe it is, but as with any question about something containing malware or being compromised or not is not about an individual using it without problems ;).