Filing I-130 in the UK -- what's the criteria?

More than likely - no, best to check with them. If I remember correctly - the paperwork for a house sale are in the pack.

All that is required for the I-864 if you are using your UK house as assets is the market appraisal from the agent and the mortgage letter showing what is owed. Our house had a buyer but we were still quite a ways from closing when we applied and had our interview.

What if either of us has a job offer? Does that count as part of the sponsorship bit?

Also, does the sponsor have to be in the state you move to (or want to move to)?

In regards to proof of UK residency, would my UK Naturalisation Certificate suffice? Or should I photocopy my ILR stamp from my old US passport?