If you had no prior marriages, then you had no prior marriages. All that is left is to let USCIS know.

Visiting my US citizen husband on a tourist visa?

You could visit if the purpose of the visit is a genuine visit and not a desire then seek adjustment of status.

New Job And Different Technolgy

If you have qualifications for both, it is doable. When employer provides training, it is always suspicious since they can do the same to a US worker.

Who has to file the 1-539 application ? am currently on f1 status and need to change the status to H4.

You should file your own request for change of status.

Would 3 weeks gap outside US under H1B affect future green card process?

Gap could be an issue. This is why it is so important that the lawyer who will be representing your employer helps you make these decision for you.

140 application was transferred to another office after approval.

There could be a myriad of reasons why USCIS decided to transfer the file.

I 485 filling separatelly?

You can file your I 485 and need not explain why you did not do that before.

When I renew for my DACA?

You do not have to have a valid passport to renew EAD in the context of DACA.

What should be the interval between the visits to USA for tourist visa?

I would say at least six to eight months if you did not illegally worked in the USA in prior visits or otherwise violated your status one you stayed.

Travel During F1 opt stem extension after H1 is applied?

I agree with Mr. Segal. DO not travel. Beyond that, talk to the attorney who is working on that I 129/H for the employer.