OnAJourney

Yes, this number is also on your payment receipt too in case you need to just check the status without logging into your account. 
 
I don't know if it makes a difference or not because I know the next set of documents will be required by NVC but bunch of people I know submitted their financial documents online right now so that the file gets moved to NVC with documents already there for review so I uploaded my Affidavit of Support, Tax Returns/Transcripts, other documents to prove our marriage already online. So you can also upload those if you wanted to. 

On that payment receipt is also your IOE number. I submitted mine on Saturday and received the Receipt# within two minutes of making the payment. 

Yes. Just scanned in the 2x2 and uploaded. Remember that when you scan the picture, it won't be 2x2 so you have to crop it to adjust before you upload the picture.