Always happy to see more people having fun with OpenBSD. Running my own set of OpenBSD boxes (although the public-facing ones are on Hetzner), so I read through the instructions and it aligns with my own experience (although I usually emphasise that most correct choices in the installer are just the default).

However, this part: "Since this is going to be a bare-bones web server we can remove most of the sets.". This is not great advice. Reducing the number of sets even on a headless server can lead to issues with ports depending on libraries Xenocara provides that would then be missing (fonts, etc.). Likewise, when you upgrade the default is to install all sets unless you manually intervene, which could lead to a surprise bump in disk usage that you may not have accounted for. In general, reducing the number of sets should be considered "I am deviating from the defaults and I know what I am doing" territory and Theo keeps threatening to remove the option to select the sets in the installer when people complain and I am inclined to agree with him. So, if you have 10GB of disk in that Droplet, just do the OpenBSD thing and go with the defaults and you will be all the happier for it down the line. Messing with the installation size really is for those rare cases (fitting many VMs on a single host, ancient machines, etc.) where you have no other choice.