You'll typically only build a settlement there if the port will provide a HUGE benefit. The 5 and 8 come up often enough that it isn't too bad, but that 11 is awful.
Since these ports were just 3:1, it is probably not beneficial for you to build there unless ALL the other options were out of reach by the time you decide you want a 3:1 port.
The picture is just an example, but I appreciate the insight.
Yes, you can settle on the corner of a single hex. Once you build road to them of course.
The rules that came with the base game fail to mention that. I'm stuck on the rule: "you may only build settlements on intersections".