Can my N400 get denied if I have a credit card judgements and bad credit?

No

I am a permanent resident in USA..I want to move in italy what do i need to become a legal resident in italy

You need to ask your question from an attorney in Italy. Attorneys on Avvo know only US law.

H1B and W-9

He will have to prove that the money is not the product of work.

Will I have a work permit?

If your sister is petitioning you, you will face a long wait before you can come to the US. You cannot simply come here on a tourist visa and stay....

Can writing an invitation letter for a friend to come visit me in the U.S. help them obtain a "visitor" visa?

You can write, but they need to qualify for the visa.

Why is it that USCIS does not readily update their field manuals with BIA precedent decisions?

Why USCIS does not update their field manuals is a question for USCIS. No attorney can answer that question. As you your problem, you should...

Is this letter really considered to be a withdrawal letter to USCIS? Is there a way I can ask USCIS if petition is withdrawn ?

That letter terminates the H-1B.

Because it is a requirement to try to avoid sham marriages.

Will they still deny me the I-751 ? What proof would I have to send?

You should file ASAP with an explanation of why you are filing late.

I forgot to file the form I-751 ,petition to remove conditional permanent residency

My colleague's advice is spot on.