How long do you think I still have to wait ?

It does not necessarily mean anything. It is not unusual for a 751 to be pending for up to 1 year.

Immigration status

There's always a risk of being put into removal proceedings for someone without lawful status in the USA regardless of marital status.

You could schedule an Infopass to your local office and get a 551 stamp in your passport.

Will i be able to renew my resident card with a criminal background?

There's no way to tell for certain without looking at the relevant documents relating to the case. I suggest you consult an immigration attorney to...

U visa

Probably means your I918 will be approved shortly.

My wife and I married the second time she visited here, she is still living with me and we are filing I-130 and I-485 for her.

I am assuming you're a U.S. citizen in which case you can petition for your step daughter.

Interview

This question has been previously answered.

Green card interview

During your Infopass, seek the assistance of a Supervisor, or seek assistance from the Ombudsman, or seek the help of an immigration attorney who...

I130/I 485 pending 2 years

An attorney can find out the cause of the delay and also work to get the case on track. Are you or were you in removal proceedings?

Is it possible to maintain Green card for citizenship while living and working outside the US?

I do not believe that you can use Form N-470 based upon the facts you have. It's not workable to meet the statutory requirements for naturalization...