Can you find the missing piece of the Porsche?

I can sizzle like bacon,
I am made with an egg,
I have plenty of backbone, but lack a good leg,
I peel layers like onions, but still remain whole,
I can be long, like a flagpole, yet fit in a hole.

It comprises roots which nobody sees,
Much taller than those trees,
Up and up it goes,
Still it never grows?

John enters a small room. The Door Closes.
When the door opens, John is in a larger room.

Explain?

Pronounced as one letter,
And written with three,
Two letters there are,
And two only in me.
I am double, I am single,
I am black blue and grey,
I am read from both ends,
And the same either way.

Twice ten are six of us,

Six are but three of us,

Nine are but four of us;

What can we possibly be?

Would you know more of us?

Twelve are but six of us,

Five are but four, do you see?

What are we?

I live in a bowl. I can swim. I have a tail. I also have fins and big eyes. What am I?

I know a nine-letter word having only one vowel.
Do you ?

I have a big mouth and I am also quite loud! I am NOT a gossip but I do get involved with everyone's dirty business.

The more you take me, the more you leave me behind.
Who Am I?