https://charity.wtf/2021/08/09/notes-on-the-perfidy-of-dashboards/
Graphs and stuff might be useful for doing capacity planning or observing some trends, but most likely you don't need either.
If you want to know when something is down (and you might not need to know), set up alerts. (And do it well, you should only receive "actionable" alerts. And after setting alerts, you should work on reducing how many actionable things you have to do.)
(I did set up Nagios to send graphs to Clickhouse, plotted by Grafana. But mostly because I wanted to learn a few things and... I was curious about network latencies and wanted to plan storage a bit long term. But I could live perfectly without those.)
I run mbsync/isync to keep a maildir copy of my email (hosted by someone else).
You can run it periodically with cron or systemd timers, it connects to an IMAP server, downloads all emails to a directory (in maildir format) for backup. You can also use this to migrate to another IMAP server.
If the webmail sucks, I wouldn't run my own. I would consider using Thunderbird. It is a desktop/Android application. It syncs mail to your desktop/phone, so most of the time, it's working with local storage so it's much faster than most webmails.