DO = District Office. Depends on where you put down on your application, thats where your DO is. Assuming you put donw Las Vegas, NV on your application AND you are still living in Las Vegas, then your DO is Las Vegas, NV. If you have moved, then you must notify USCIS.
SS# is totally different from EAD or iEAD. I am not sure about how SSN works with your B-1 pending AOS. I got my SSN when I was a student. B-visa are for tourist/business purpose. Depends on how long you entered the country before you get married and how long after you entered the country you filed for AOS, you might/might not get your AOS approved. B-visa is a non-immigrant visa, so if you get married within 90 days of your entry to US, USCIS might not like that. But again, I'm not a lawyer, and I can only tell you what I have read and what I have heard.
Keep me posted. I will be checking this thread on and off on Monday, 2/6/06.