Lrsouth

I guess I am just lost on what to do next.  I have filed the ds-160 form online and I am not sure if I will be receiving a confirmation email saying the application was approved or how long I will need to wait.  Also, when do I need to pay the K1 visa fee?  I don't know if i need to pay it now or wait until his visa is approved.   Also, the I-864 form doesn't need to be mailed in, does it?  I have read many things and every thing i read tells me something different.  I am just lost and I hate not doing anything to prepare for this visa.   

My K-1 fiance visa petition was approved my the uscis and was sent to the national visa center where it has also been approved and is ready for the interview process.  I have tried to choose an agent, but it won't allow me because I do not have my invoice identification number and I do not know if it will be sent to me via email.  It has been ten days since i have received notice that I can begin the visa processing.  I am confused and cannot seem to find any answers.