This question is long (4 questions), and we normally prefer to keep questions to
1 question per question. The 4th is also opinion-based enough to be off-topic.
However, the questions are related enough and I have enough to say that I'm
going to (try to) write an answer.
Your questions first:
Does this mean that at this point in time, argo and bufdo ...
From :help arglist:
If you give more than one file name when starting Vim, this list is remembered
as the argument list. You can jump to each file in this list.
Do not confuse this with the buffer list, which you can see with the
|:buffers| command. The argument list was already present in Vi, the buffer
list is new in Vim. Every file name in the ...