Uhhh alot of questions.
1) You will keep all your retainers and whatever they have, dunno what happens if your retainer name is already taken though. But you need to not have anything on the market board.
2) Map/Quest will be left intact.
3) Not sure about now, used to be 1 mil on you, and like 100k or something on each of your retainers. Convert extra gil into materias/craft materias/vanity crap
4) Keep all GC rank/seals