I have 2 previous E-2 visa denials. I'm considering an F-1 visa. How should I approach the visa interview?

It does not sound like a good idea. Given your 2 denials, it would be best to hire an immigration attorney to evaluate your options.

Can H-4 visa holder work outside the US?

Yes she should come in as H-4 and that have no impact on her job in Singapore.

Extend the B1/B2 visa for 9 more months

You need to consult an immigration attorney immediately. Generally, a tourist visa will not be extended for more than 6 months. It does not sound...

Can a green card holder invite future spouse?

It is very unlikely that she will obtain a visitor visa. It may be best to marry her in China and come back to the US to file a petition for her....

Records

You would need to file a FOIA request.

Can a conditional green card holder travel outside the country for a few months?

You are able to travel abroad with a conditional green card but be sure that you do not remain outside of the US for more than 6 months.

L1 to H1 Change of status with one week gap

It is best for you to go to Canada to obtain your H1-B. Consult your employer's immigration attorney.

Does tax penalties and credit card debt prevent me getting a green card?

I agree with my colleagues. It should not have an impact on your green card application but it is best to consult an attorney.

Do i have to still include her birth certificate in the package?

The certificate of naturalization should be enough but I would bring her birth certificate to the interview.

Selected as the best answer

Should I bring to my green Card interview a document that show I haven't had any criminal record on my country?

If you have no criminal record then you do not need to bring anything relating to that to the I-485 interview.