rsd

There is only one form on the plane now--customs declaration. Everybody fills that one out.
Which line? You are still a British visitor, so Visitor line. You might want to ask an attendant if there is a special line for new immigrants. A few airports might have that.

Hah. Nice gif.
Hey, let us know what happens! London is one of the more lenient, human, consulates to deal with by the sounds of things. Good luck. I'm sure it'll be okay.

Was this something that you were required to do?
I assume so if you're doing it, i'm just not familiar with these issues.
I would think you'd be denied until you come back and provide the paperwork as proof.

OK, I've not seen this particular requirement or issue before, but what I have seen is someone missing something the interviewing officer wants to see (I wish I could recall what it was now - I think it was some form of relationship evidence).
In that case, the interviewing officer had approved the case contingent on the applicant sending the required, missing, documentation. I don't think you'll get a flat denial, I think you'll get the opportunity to add the missing document if the officer believes it is required to approve the case. I think they held the passport during that time, then issued the visa on receipt of the documents.
I'd just wait and see tomorrow, to be honest. Perhaps take a copy of any correspondence you've had with the insurers to show that the documentation is the the mail etc. I've not heard of someone requiring to show they had adequate insurance for an on-going medical condition, so I don't know how vital that is to visa approval. I assume your medical results were sent to the embassy? That's pretty important.

I HAVE seen one case requiring insurance.
I don't know what the result was, but they "denied" them during interview until proof of insurance was provided.

The first medical questionnaire you fill out is in this document. http://photos.state.gov/libraries/unitedkingdom/164203/cons-visa/iv018a_medical.pdf
Another is filled out at the exam. Generally if you have a chronic condition, Knightsbridge may ask for a statement from your GP detailing your condition, onset, treatment, meds, prognosis., etc. Some save a delay by getting that ahead of time and bringing to the medical exam. It shouldn't affect your visa.

Sounds great.
Have her check two things.
1. You don't actually need a SSN to be on an insurance policy. Babies go on insurance before they have SSNs, for instance. You might need to have her ask someone higher up, as punching the SSN is the most normal protocol.
2. Make sure that you immigrating will be considered a "life event" to add people - it should be, but usually a person is added either immediately after marriage, or during an "open enrollment" period. Make sure you don't have to wait for "open enrollment."

Showing that you can get on a health insurance plan immediately upon entering the US will make the problem zero. The only question that will arise is if you can pay for it.

I definitely wouldn't lie at the medical, and if you have any previous conditions I think it would be a lot better to tell the doctor about it rather than try to hide it. If the doctor gets suspicious or catches you in a lie, they can make a note on the medical report, and that can definitely affect the visa. As long as you're truthful, and don't have anything communicable, you should be fine. They're more worried about things like TB or syphilis.

I want to know the story!! hehe

You didn't live there, leave it off.
If you have any doubts call ACRO Customer Services on 0845 60 13 999, they are very helpful