Talk to your DSO. I do not believe there is any rule against having an I-20 issued if one has an I-140.

You can respond as soon as you wish. You can request USCIS to expedite a petition.

Yes, you can notify USCIS that you do not wish to change status to H1b.

It depends on the exact timing of what they filed and when. Find all of their records and show it to a lawyer.

If you plan to include him in your tax return for this year, he is a dependent.

Yes, you could do that. Or get a reentry permit.

It is better to wait at least six months before changing jobs, even if you filed over six months ago.

It depends on what information USCIS received about you and whether they match it with any future filing.

Send a letter to USCIS and request them to extend it.

If there has been a finding of paternity or if he has accepted paternity over the child, then you should name the child.