I think they are meant to be like expensive way forif people needed to finish up a character and were short on frags but the characters they sell there should probably be updated
This is correct
It's intended that way to help players who feel they need to rush completion.
As for the ninjas themselves. Eventually, they'll be added more. As for when?
There's no ETA on that and I can't promise things that I don't know.
Hopefully, this helps!