Would it be OK to travel internationally with only the i-551 stamp on my passport and reenter with no problem?

It would be ok to travel with I-551 stamp in your passport.

Can a permanent legal resident (gc holder) marry and bring a foreigner spouse into USA?

You cannot bring her directly. She would fall into F2A category and they are currently processing those filed in early/mid 2014.

Citizenship interview

Given unknown arrests and dispositions are involved in your posts, it is impossible to predict.

Will my newborn baby get a u visa at the same time as me?

Once you are approved you can file an i918 for your derivative newborn. No way to tell if you will be approved for 2017.

Can my parents visit on B2 visa (which is already issued to them) as I have sponsored their last visit but currently I'm on H4?

Yes the B-2 allows them to come to the US.

He needs to successfully apply for a B-1/B-2 visa. You can send him an invitation, but what it is most important is the proof he provides regarding...

Would there be anything in the way of getting residency status ?

You will have the normal responsibility of proving a good faith marriage by providing document evidence of a commingled marriage.

For CR-1 visa, how many originals do I need for the police certificate?

One original but you will need to provide a copy to both NVC and the embassy.

No you are not a legal permanent resident of the US. You may be considered a resident in terms of where you live, but you are not a US LPR.

1. Can I add my spouse to my Canada PR from US? 2. how much time does it take for adding her?

You will need to address your question to someone in the immigration Canadian bar.