It depends on whether you pronounce the letters individually.  The a, an entry: Use the article a before consonant sounds: a historic event, a one-year term (sounds as if it begins with a w), a united stand (sounds like you).

Use the article an before vowel sounds: an energy crisis, an honorable man (the h is silent), an homage (the h is silent), an NBA record (sounds like it begins with the letter e), an 1890s celebration.

It's clear either way. 

If Mid-South is a widely used term in that area, go with that. Otherwise, mid-South.

AP wouldn't abbreviate this in any way.  Here is the previous answer to a similar question, about data communications:

We don't have a style for an abbreviation for data communications (our style would be no abbreviation at all).  The fact that you found so much inconsistency in your search indicates that the question is, indeed, unsettled throughout the industry and there is no single correct answer. If it helps, a few similar examples from elsewhere in AP style: We use dashcam as shorthand for dashboard camera, and bodycam in some situations for body camera. Thus, datacom (no capital letters) might be a good choice if that makes sense for your audience(s). Consider what is likely to look right to your biggest audiences. Then be consistent in using what you choose.

Thanks for noting this. Indeed,  and contrary to my previous 2017 answer, we go both ways in headlines. Some headlines spell out ordinals under 10; others use numerals. We generally do allow a bit more flexibility in headlines because of space constraints. Either use is fine.

Written words should be quoted in the style in which they are written. Here's the relevant part of the quotations in the news entry: 

When quoting spoken words, use AP style: No. 1, St., Gov., Sen. and $3.

When quoting written words, retain the style used by the writer; do not alter the written words even if they don't match AP style.

That could be argued either way. AP stories use players' union.

That should be lowercase.

With digits. To be clear, you could add a parenthetical: "60 (thousand) or 70,000 people." Consider whether it's truly best to use it as a quote, since indeed it would be less awkward to paraphrase. 

If that was the formal and full name, uppercase it. If it was an informal name, or part of a longer name, then lowercase it.

The phrase so-called takes the place of quotation marks in these uses. So you use one or the other, but not both. In an ideal world, every AP staffer would know and follow every style rule. That's certainly our goal. Alas, it's an imperfect world and some style lapses do slip through. In the example you're dealing with, I'd go with so-called, no quotation marks.

AP doesn't have a detailed style on the use of en dashes and em dashes. In general, we use hyphens to link words. However, I wouldn't use a hyphen in your example because the result could look like a compound modifier. Can you rewrite it as the relationship between morbidity and age ... ?

We'd say: ... a doctorate in psychology. Also, note that the abbreviation is punctuated differently: Ph.D., Ph.D.s

We avoid unfamiliar abbreviations for general audiences, so we don't use any of those. Instead, simply information security.

If the shorthand is very familiar to your specific audience, check to see if there's a predominant style used by others in the industry. If it helps, a few similar examples from elsewhere in AP style: We use dashcam as shorthand for dashboard camera, and bodycam in some situations for body camera. Thus, datacom (no capital letters) might be a good choice if that makes sense for your audience(s). Consider what is likely to look right to your biggest audiences. Then be consistent in using what you choose.

As an adjective, AP stories use wood-burning: a wood-burning stove. In other uses, adapting Webster's woodworking style would work: My project involves woodburning.

We call hurricanes Harvey and Irma (as well as Maria and others) hurricanes because they are, in fact, hurricanes. There's no reason call them superstorms when the descriptive and correct term hurricane covers it.  Adding the category, such as a Category 4 hurricane, bolsters that description and is very specific. Sandy, on the other hand, was a hybrid storm that didn’t meet the meteorological definition of a hurricane or tropical storm. It was informally dubbed a superstorm, and that stuck.

In AP stories, the terms are limited to direct quotations and spelled lowercase. 

AP doesn't issue guidelines on formatting press releases. Have a look at publicity services, such as PR Newswire: http://www.prnewswire.com/

We don't have a specific style for that. What you have is clear, though I might put the event description as the second entry (after the name of event).

I agree that nondegree-seeking doesn't work. I'd hyphenate as a compound modifer, for clarity: non-degree-seeking student. 

Capitalize the first word of the quote if it's a full sentence, as yours is. If it's just a phrase, lowercase it.

Western Front.

It's correct as you've written it. For more than two cities, try: We provided services to XYZ's New Jersey locations in Belleville, Branchburg and Boonton.

We considered it last year and decided to stay with health care. We will consider it again this year.

A plural verb for the Emmys, the Oscars and the Olympics: The Emmys have been televised ...