Nope. The astral plane is a completely real and independent realm, just like the physical world (and even much bigger than the physical universe).
Yes it is. Plus around 20 other books. See the book recommendations I posted here: Official Astral Travel Thread - #3 by JAAJ
That silver cord is pretty much indestructible and can stretch through the whole universe. It will only break when your Higher Self decides so a.k.a. when you die.
Do not visit anything government or alien base related in your astral body while you still have a physical one 
That was also mentioned in one of his first videos on the channel. It is still online.