Once I get an O-1 visa and SSN, can I work for anyone or do I need to have other petitioners if I work for other companies?

The O-1 is typically employer specific unless you have an agent who petitioned for you.

Green card interview went well but no decison made on the spot

Was there an issue raised at the interview? If not, then you need to be a little patient.

I would definitely contact the USCIS at 1-800-375-5283 and advise them of this.

I would like to know whats my waiting time to apply for my citizenship and how can I do it?

you can file the naturalization case 4 years and 9 months from when you received your permanent residence status.

Form G-325A, my husband was getting workers Comp 1.5 year ago should he write that on the form or just put Unemployed?

You do not have to list that he was getting workers compensation. Unemployed is fine.

Will I still be a US citizen and travel freely back and forth even if I moved to Ethiopia?

Once a U.S. citizen, then forever one

Cancellation of Removal

He would most probably be able to complete the process in the USA.

How to get expert opinion based CV (Education, papers, awards and patents etc), on qualification for Greencard under EB1

We can provide you with a list of such experts. You can also try The Degree People at www.thedegreepeople.com/

Do i have to go back to my home country or can he petition for me and i apply for adjustment of status from here?

You would not have to leave as long as you came to the USA with a visa regardless of when ou entered the USA.

What is the timeframe to become a Green Card holder if you marry a US citizen?

In New York, it typically takes 4-6 months after you file the case for you to gain your conditional green card based on marriage to a USC.