How long can i stay after my I-94 expires

Your statements are not clear. If your H1B approved and no change of status approved, you have to depart the country as quickly as possible and get...

My L1 visa expires in 20 days. I have a letter from USCIS where it mentions I have an extension for a year.

What letter you have, do you mean an extension of stay approval in form I-797.

Can I apply for EB2 visa?

Yes... you can still file, today CBP has confirmed that the EO does not affect who are currently in the country. Further you are an Indian citizen.

Switch employer when H1B extension is pending with current employer

What is the validity of your current I-94/I-797, if it is still valid - it is straight forward transfer. If expired, you can still change employer,...

Sponsor for green card based on marriage.

pls check https://www.uscis.gov/i-864p for income requirement

Can I file H1B extension after 6 years on approved 140 from previous employer??

Yes.. you can use your approved I-140 from any employer to file extension beyond 6 years.

Question regarding H1B Extension and i140 already approved - before maxout

I-140 has nothing to do with the validity period of your H1B approval. Employer must establish the availability of the job for the requested period.

Hindu! no special advantage... still need I-140 approval to get H4 EAD

Will i need to retake biometrics again

Yes, Naturalization application needs separate biometric.

You need employment authorization to begin employment, no other shortcut. He may request for expedite process with a valid job offer and economical...