Take a look at Tuta

I do not think that any solution will satisfy everyone. the limit of 35 days is probably a bit short.

Paying for upgrades was popularised by apps on Apple devices. I remember a time when upgrades were free for life.

You can pause and schedule update on Windows

Any flatfile cms should do the job.

You could try https://automad.org/ and setup up a password page to keep it private. It’s super simple to maintain and secure. You just need a vps and a domain.