How much time it takes to change status from j1 to f1?

You do not need to apply again as you say but you must get an F visa in your passport with your I-20 authorizing student status.

When I travel out of us using I551 , will it stop my green card processing and posted to my address?

As long as you return with a valid I-551 stamp, you should be fine. This assumes you are not leaving the US to live abroad.

Carry valid green cards and your passports. You should be fine.

Interview completed but case must be reviewed

My advice is to "sit tight". It most likely means that the FBI background check is not complete. This is normal.

I applies amendment for location changed and got RFE and i travel to India ,if i get rejected as RFE result?

Do not leave the US until your RFE is approved. If denied while you are outside the US, you will not be able to re-enter.

For L2 EAD, does the application start from date USCIS receiving the form or after receiving the case number. Pls clarify

The date on the USCIS receipt, form I-797.

During my H1B visa interview which resulted into administrative processing, I am asked to submit i-203. B?

Seek legal assistance since the facts are insufficient. Normally, your employer's attorney would be helping.

Submit i485

You should probably have an attorney assist you. There are more proofs and forms involved than those you listed. You can check online at...

If you are paroled in united states and have withholding of removal , can you adjust your status through employment ?

You need an employer to sponsor you for a nonimmigrant visa from which the employer may want to sponsor you for permanent residence.

While there is no guarantee this will work, getting a sworn statement (notarized) by that notary as to what happened and his/her mistake, should be...