try the different entrances like the one in golden wood and the one east of wispy tower for example. Then to open the chambers you need a certain amount of badges for each door.
no problemo
i guess you already finished v12 content by now, but when the game autosaves you can just go to your save folder and search for your last save file to rename and then load it.
does anyone know how to reach the western part of the castle after the karen event? i can see some items there and can walk on the upper floor of what seems to be a library.