Do I have to send my proof of domicile to nvc first. Or is it enoph do bring them to the interview overseas

The letter from the NVC should say whether they are holding your application until you submit the evidence or if they are forwarding it to the...

Profit to Non Profit

Since you have been counted against the H-1B cap already, you are eligible to "transfer" to another for profit company later.

How long after getting married can an undocumented immigrant file for a medical card and/or is there any cancer care for him?

Get married right away and have him adjust status via a one-step process. Then he will be an LPR, covered under your insurance.

Can I become a guardian for my nephew?

you would need to adopt him before he is 16 and he would need to have lived with you for two years. more information is on the USCIS website,...

Can I sponsor my husband for a green card even if I don't have a domicile in the United States currently ?

You will need to find someone to file the affidavit of support, unless you have sufficient assets or income/job in the U.S.

What is the easiest way to move to the US without a relative or masses amounts of money?

Depends what you mean by masses amounts of money, also depends on what passport(s) you have. You can look into getting a student visa, or a J-1...

How can my British Fiancé become a permanent resident, even though I am a DACA recipient?

She would most likely need to look into either employment visa or student visa. There are too many possible options to go over all of them here -...

Will I be able to work for a private company under my EAD when I change my visa from L2 to G4 to work for an int. organisation?

once you change status you will no longer be on L2 and therefore your EAD will no longer be valid.

Interfile your spouses I-485 with your pending case.

Will any of the following tax/extra income negatively impact my Green Card?

If your question is are you working without authorization, it looks like you are not. All you describe above seems to be passive income generated...