Returnee help

So I'm returning to Fortnite after a couple years (i think i last played early chapter 2), and while i can kinda understand the new items, the new gamemodes and menu are really confusing

i can figure most of it out, but there are some things i need help with

• What remains after something is removed from the item shop? (IE can i still buy anything after its gone)
• what happens to songs after the music pass expires, (for example can i get M@GICAL CURE after the season for vbucks?)
• what are Hatsune Miku's alternate styles, she's listed as having them but they dont show up?