every provider who supports aliases.
like foo+baa@bzz.tld where everything after the + is exchangeable. so you can use a 'different' mail for every service you use and just block where spam comes from via the alias.
Matrix i guess, its a federated messaging protocoll. Flagship messenger app would be Element.
Sending large files would depend on the server you are on.
In terms if logging: sys journal does the job for me ...
I do run prometheus + grafana for some services but that is mostly for some fancy looking graphics nothing really usefull.
I would recomend you to monitor updates of you apps so you are well informed when und what to update (i just have subsribed to all the diffrent release git rss feeds)
I only know German ones: senfcall.de or bbb.digitalcourage.de