[Q] Some questions about my Kindle Fire HDX 7

Hi there,
I have a KFHDX 7 with Fire OS 4.5.4.

1 ) Currently, it's impossible to root with this version, right ? How downgrade ?

If it's rooted :
2 ) Is it possible to install a new rom ? like nethunter ?

3 ) We can install .apk from android store with a drag'n'drop ? (I haven't see the similare version of moon+ reader between amazon store and google store :-/ )

Thanks in advance,
Kind regards,
Sqdz'