Nagging Questions

[Mattius]

I have a few nagging questions in my mind-

Why was Feanor such an idiot, I mean sure he was good at stuff but as soon as Morgoth took the Great Jewels he defied the Valar. Surely with patience the out come would have been the Valar going to war anyway. This leads me to my next question...

Just how many noldorin elves were there that came with Feanor and Fingolfin back to middle earth? Are we talking hundreds? thousands?......... millions?!

Also did Arwen actually BECOME mortal or did she remain an elf and die of greif after Aragorn's passing? I heard another view that because Elrond was half-elven then when he left middle earth she would become a mortal.

Last of all, is there any information on the child/children of Aragorn and Arwen?

Thank you, these are just a few nagging questions I have i'm afraid!