score:3
Question 1.
Your conference is in Ireland. Ireland being the principal destination of your upcoming trip, you'll apply at the Irish consulate in the US (your current and legal country of residence). A list of Irish consulates is found on this Irish government website. Where you live in the US will dictate the consulate to which you apply.
Even if the Irish consulate says they don't want the original annulment letter, they might change their mind during the application process. With two months to go before the Irish conference, time is getting short.
To maximize the chances that you'll have what you need:
Question 2.
Visa examiners are interested in relevant facts, not extraneous facts or emotion.
Your explanation should contain the relevant points, and no extraneous or unnecessary material. The explanation should be emotionally neutral, and it should not read as whining or wingeing, seeking special treatment, complaining about what happened, or self-abnegation. The explanation should contain the necessary facts, and be as short as possible.
For instance, in Section 1 of the first part of your question, all the words after "Istanbul" are superfluous and can be omitted. The only relevant points are that you had a long layover in Istanbul, and were questioned about your itinerary. The matters presented in the Section 2 can (and should be) similarly limited and condensed, with emotion and self-abnegation removed.