Thank you, I'm glad it helped! I have visa in hand, counting down the days until I move.
1. There was no follow up with her employer. The letter was purely to get the embassy to agree to following the DCF process, and they accepted it with a summary of the situation.
2. No issues, but we went above and beyond, providing each of their tax return documents for the last three years, as well as my wife's. Maybe overkill, but better safe than sorry.
3. A. I have been able to travel freely. I had an ESTA already so was able to travel to the US between the I-130 approval and the visa interview. I have also visited the EU without any issues - I don't even think the border police noticed I had a US visa as it's not relevant. Just make sure you have valid passports/visas to travel to those countries!
B.My wife returned to the US shortly after the initial I-130 submission interview. Her UK visa has not expired yet.
If you submit the I-130 before your visa expires then you will be fine, even if you leave the UK afterwards, because your work will be done. You will not need to attend anything else, only your spouse.
It is imperative that you contact the US Embassy in London ASAP to confirm you can proceed with DCF and get an appointment to submit the I-130. Good luck!