Apple - How to share directory over NFS from Mac? (w/o macOS Server app)
What was required was the following line in /etc/exports:
/path/to/shared/dir -mapall=<uid of local user on host machine with correct perms> -network 192.168.56.0 -mask 255.255.255.0
exports(5) is the FreeBSD version, obviously. Once I did some googling for the solution with respect to "FreeBSD" instead of "Mac", the necessary information presented itself, the a colleague pointed out the exact flag needed.
Source: http://www.freebsdmadeeasy.com/tutorials/freebsd/using-freebsd-nfs.php
NFS Manager was helpful in validating the solution but not necessary.
macOS Server is not required at all to share directories over NFS. The macOS client provides all necessary tools.
Testing various exports with bogus paths, I'd assume your path simply doesn't exist.
The most convenient GUI-tool for NFS is NFS Manager. You will be presented with a nag-screen launching it or changing configurations, but it works without further restrictions.
Most of your desired options are available in macOS (check man exports) and can be configured with NFS Manager:
Some details have to be configured in the advanced options (e.g. the access permissions).