have a temperamental internet connection at home

Love this description. :D

I don't use Fedora or dnf, but looking at the manual on https://man7.org/linux/man-pages/man8/dnf.8.html I could find following:

 dnf [options] upgrade <package-spec>...
              Updates each specified package to the latest available
              version. Updates dependencies as necessary. When versions
              are specified in the <package-spec>, update to these
              versions.

dnf [options] upgrade-minimal
              Updates each package to the latest available version that
              provides a bugfix, enhancement or a fix for a security
              issue (security).

So I assume you can just specify which package to upgrade only.The minimal variant does not support specific packages, but maybe a good idea to get all important stuff in one batch first. Then the general upgrade command would have less work to do I guess. At least here on the Arch side, upgrading a single package is absolutely not recommended. But I don't know how dnf handles this.

Also on Archlinux with pacman each package gets downloaded before the installation process begins. So if your internet goes away while downloading, it does not matter, because next time it will only download the rest of the packages and continue from that point. And it only starts installing locally after everything is downloaded from internet. Now, as said I don't know how dnf handles this, but would assume it does it similar.