Dokuwiki (dokuwiki.org) is my usual go-to. It’s really simple and stores entries in markdown files so you can get at them as plain text files in a pinch. Here’s a life lesson: don’t host your documentation in the machine you’re going to be breaking! Learned that the hard way once or twice.

For reverse proxies, I’m a fan of HAProxy. It uses pretty straightforward config files and is incredibly robust.

I can’t give direct experience here, but this is exactly the use case I’ve been meaning to spin up mailpiler for: https://www.mailpiler.org/. One of these days that will rise to the top of the priority list.

If you want an image, it doesn’t matter what the underlying file system is. You should be able to use a tool like Clonezilla and get a 1:1 copy. Depending how you’ve set up partitioning, you could also use sgdisk to set up the proper partitions and zfs send/recv for the new data portion of the drive and install a boot loader. That’s probably the way I’d go in this instance.