Hrm, time for answers for what I can:

Don't know how to run fullscreen, I personally hate that setting because I alt-tab too much so I never looked at it

The colored parenthesis are the auto-translate function. You press tab when writing if i'm nto wrong to pull up a list of therms and select one. Whatever is in colored parenthesis is seen by the other players in whatever their native language is. Useful to talk to people from other countries.

A normal player can find that out, I presume it was found out by trial and error and isn't there a tutorial of osme sort? Never did gathering myself

By throwing elemental abilities at it, if you notice a specific element deals a lot more/a lot less damage, it means it's a good/bad idea to use it.

This part should answer that, I believe

Second verse, same as first. Mostly, for advanced help you'd need to ask other people, I guess.

There probably is, but it's old. You'd need to search for it

Ugh- A pain, but a lot of acronyms are brought over from XI and they are more often than not user-created so it doesn't helps. The classes and jobs have official acronyms that are visible somewhere but i'm not sure where, i'm sorry
To answer you direct questions, WS stands for WeaponSkill, which is basically a TP-based offensive move. AF is a completely player-created acronym to refer to job-specific equipment, it means 'Artifact' which is not the official name, but it is also the one the community adopted.

Not really, but usually those that you learn later will deal more damage, you just need to check what they do. Presumably due to the combo system you're going to use them in sequence anyway.

Not that I know of, sadly. I wish there was

Depends on what your target scheme is set for in your options, there's a command for it that should be shown somewhere in your keybinds.

Theoretically with the Enemy target filter you won't cycle targets on yourself, but can still target yourself by clicking.

Factions are for special leves, really, which give special rewards