How can I change from F-1 OPT to H-4 EAD without gap in employment while in the US?

I think you have enough questions and concerns to warrant a consultation with an immigration attorney.

H1B approved, not stamped on passport.

Neither situation would require you to leave the country. A stamp is only required to return to the U.S. If you don't travel, no need for a stamp.

Will I be having problems entering back the United States?

You will currently not have any issues but things are changing so fast recently, it is hard to know what may happen in the future. The Philippines...

Filling out I-539, Part 3 1a as "Extend the stay unitil____? is it ok to leave this space blank as my I-129 is still pending ?

No, your employers attorney would have requested a new expiration date for your extension. You should see if they can assist you in filing the H-4.

What does that mean

Unless the update was in error, it means that your case has been approved and the residency card is being made.

I was arrested yesterday in my dorm room for possession of marijuana and I am on an F-1 visa. Will this severly impact my status

You need to consult an immigration attorney who can provide guidance on how this may affect your future.

Can I apply for my Wife H4 extension if her h4 visa and I-94 is expiring in sep2017

She can file for an extension and receive up to your expiration date on your new approval. It's always best to file both petitions concurrently or...

First, you need to consult an immigration attorney as these are serious issues raised by your questions. The H-4 status for the spouses will...

I have a wife that we divorced 3 years ago when I got to USA . I married to USA citizen and I got legalize in the USA.

Not only will you have to prove that the new marriage is legitimate, you very well will have to be able to establish that the marriage that...

Sorry to hear about your mothers health. Currently there is no regulation that would prevent your entry but that situation can change at any moment...