Nextcloud is feature-rich, but a little slower and vastly more complicated than a CalDAV server like Baikal.

Use a hardened-by-default OS like OpenBSD, HardenedBSD, or something similar in Linux.

Uh, can’t you just log in to online banking through a browser? I can.

OpenSMTPD. I run a private mail server for family, and it works flawlessly. No maintenance aside from backups and occasional OS upgrades. https://poolp.org/posts/2019-09-14/setting-up-a-mail-server-with-opensmtpd-dovecot-and-rspamd/

Grep. If you have the sources digitally and local, you can just run a search for a string.

Don’t use Outlook for non-Outlook email services. Problem solved. I am required to use Outlook for my work email, but I keep all of my personal email separate, accessed with FOSS email clients.

Care to elaborate on the significant downsides?

If Hugo stops working down the line, you can compile your markdown with something else. Simple is king!