Immigration question.

A self petition as an artist in the first presence is permissible. This has a very high standard and you should speak with an immigration attorney...

I filed N-400 may 2014 , did my biometric and received a yellow letter with some required documents includes my passport

You will need to establish the you maintained your residence in the US.

If the marriage is legal were occurs and the marriage is bona fide not simply for resident status (green card) it is possible.

H1 B employer intending to fire me

Yes termination is permitted unless there is a prohibited employment practice. The employer may be responsible for yout reasonable transportation...

If I currently have TPS as my status

EAD based on TPS is not dependent upon I485.

H1b extension-after 6 years - changing job

New employer needs to file for 3 year. H1b and file a new PERm right away.

Employer change after I-140

You may extend the H1b but need the 485 pending 6 months for portability.

You may be permitted to refile. This time consider using an immigration attorney if resident status is important to you.

L1B to H1B approved - option to continue in L1B

If you do not change to H1b and have continuously retained L status and your spouse has maintained L status, she continues to maintain L...

What is the processing time for performing a COS from H4 to H1B? Is premium processing available and what are the lead times?

You do not need an employer to change from H1b to H4. Premium processing is not available for a change form H1b to H4.