No advice given here is going to be entirely universal, but I'll try to keep it as general as possible.
1) People either walk around and talk to each other in character, or at events/normal gathering places.
2) In game I don't think many people use the mic to RP, its all via in game chat though some roleplay FCs might do it over mic in their teamspeak/discord
3) As the main story is focused on the warrior of light and their specific journey, *in general* its considered poor form to RP that you are the warrior of light or that the story is IC for you. this will vary between groups greatly tho, and other content some people will roleplay while doing in some for or another (such as dungeons or things like that)
4) Events are just things that are announced for everyone to gather at, but on the RP servers there is usually people RPing almost all the time at say the quicksand, or in various Linkshells/Free Companies.
5) IMHO, yes but ymmv
6) same as 5
Hope that helps!