To answer #1 invites opinion; I believe there are special forums for polling and/or "popularity contests"
As for the style itself; the first rule of English prose style is the same as that for writing code - HAVE A STYLE.
For myself, in answer to #2, lacking specific guidelines or requirements for style I would use Associated Press (AP) Style. My preference for it derives from reading books and periodicals as a youngster growing up...also I had it shoved down my throat in college so it is the style with which I am most
AP Style develops continuously. It is designed to optimize readability, clarity and brevity. When new acronyms, words and slang make their way into the zeitgeist, AP determines a style to use for each. A stylebook is handy when the writer hits a grey-area; like the Federal Bureau of Investigation. (Is it "F.B.I. ...FBI... do I spell it out on first reference?) Normally we spell out acronyms on first reference and append periods in-between on second ref. If an organization or acronym is "common enough" ... your stylebook tells you how best to communicate it to the reader. In the example, "the FBI" is considered so well-known that the abbreviated form I used on first reference is a-ok. Note also that common acronyms like CIA, ISIS (or is it ISIL?) USMC, NBA, NFL, DVD, IBM and others appear sans-periods between them. They may or may not require a spell-out on first reference. This is just one of 100s of reasons to learn, develop and use a style.
To tackle question #3 ("number three" in AP Style) professional writers use AP Style as a template format. It could be stand-alone (for a solo project), or if writing for a technical guide, journal, brochure, site (....) your organization will also have a set of style rules to augment AP and fill in all the "grey areas" for industry-specific abbreviations, terms, definitions and all that good stuff. The same goes for a series of fictional tales, you may decide to create your own style--unique to your own fictional world in order to give the story a more creatively-structured feel. Pay special attention to the style used for versioning (documents, labels, presentations) and the style company editors use when a document is routing...that is, how they markup documents for errors, changes, suggestions, questions and the like.