What happens to a tourist visa (B2) once the immigration process begins?

Reentering on the visitor visa while you ha e a pending marriage based case may be difficult.

My I130 folder was losted from my immigration folder ?

You should schedule an jnfopass appointment to discuss whether refilling is necessary given USCIS error.

Yes you may do so however the chances of being approved are limited given your previous history. Consult with an attorney for guidance.

How long does it usually take when case has been transferred to another office? And is this a good thing?

Transfers may happen and it does not indicate anything one way or another. It can be a few months after transfer until decision is made.

I am an American citizen and my fiance is Israeli.

Yes you may marry however it can not be your fiancés intention upon entering to marry and subsequently adjust status. You will likely need a...

NIV indicates non immigrant visa whereas IV indicates immigrant visa.

I-485 approved after an hour of the interview And I don’t know if I pass the interview or not?

If the I485 was approved then you passed your interview.

What other steps can I take to get an answer from USCIS ?

This is within the normal processing times so unfortunately there is not much that can be done to expedite the case.

What can I do?

More information is needed about your case including your current status, your manner of entry, etc. consult with an attorney for guidance.

N400 interview while I751 pending?

You cannot do anything to ensure that but can certainly request both interviews be conducted at the same time and the officer may comply.