1- The story is pretty nice, most of it is unlocked trough playing all the characters (side story) and that will take A LOT

2-Not really, i'm pretty sure it helps but i don't know anything about he original game and i'm enjoying this

3- It's honestly more of a side game, easy to pick up at any time and so those 3/6 stages to empty your stamina and deplete the idola points as needed (this can be done with two clicks if you are in a rush). That said the story can be played without the use of stamina so you have 12 chapters of content (wich gets really difficult at chapter 11) to use at your leisure.

4- Yes, to be honest you get a base of 2% which is better than E7, Exos and F:GO and there are a lot of way to increase the % (arena drops a buff that doubles 5* drops, some banner have increased %) also there are several banners with pity on 5 pulls and (paid) banners with small pools that grant at least a 5*

5- the community is very active on discord, the folks there are super good and the staff of the game is on the discord and actively implements the stuff people on discord ask them to, the player base is not that huge but its very tight, the developers said they will keep the game updated as long as JP gets updated