Welcome to the forum Joe
I have to agree with Brian (Grump). Whilst the extensive information you have provided is correct it is largely irrelevant to either pen making or the common threads that members are likely to come across in modern machinery and motor vehicles in the real world on this side of the Atlantic in the 21st century.
I have a variety of taps in UNF, BA, BSP, Whitworth and metric sizes. the only ones that get regularly used nowadays are the metric sizes.
Fountain pen nibs have metric threads so in that context any other standard is irrelevant.
So to get back to Andy's original question. For occasional use a cheap set of metric taps and dies from Lidl or Aldi will suffice. If you intend to use them more regularly then you might want to pay a little more for something like this set from Cromwell Tools. Unless you are a full time engineer you will not need anything better.
If you plan to use them for making kitless pens then I suggest you read this tutorial by Mike Redburn on IAP.