Falainwest,
I am not conversant with Affidavit of Support but it`s the right thing to do, by starting immediately so that if there are any errors or unwillingness from the person to sign the Support then you can switch without delay.What I know is that DV winners dont need an Affidavit of support(German case). But in order not to jeopardize the situation some DV winners go for it just to make their financial situation solid. If that person is willing to sign for you then,that form is the right one. What most people do as I have read in other forums is that,the person signing the Affidavit simply writes a letter accepting to receive you and would be responsible for you untill you become independent. That letter "may" include other information if necessary annaul income and probably tax sheet.You will attach the letter to your file for the interview.This option is workable especially if you yourself has a solid bank statement to show, that is above the poverty guideline for the state you intend to immigrate to.
What is circulated online about the AOS issue is inconsistent. I can only speak for myself. For myself ,I had a family of 4 persons and based in Germany. I know that people in America would not find it easy exposing their financial status and in addition would not have time to run up and down following documents, what I did was I simply made my bank statement solid that would take care of all the family members when in the US. And was above the povertyguideline,I tried to get the AOS just to put more weight on my file but couldnt just because of the above mentioned reasons, but I encouraged my host to write a letter accepting to receive us and willing to support us in terms of hardship, which he did but under hard struggle.The letter was emailed to me just on the eve of my interview. I printed it out and attached it to file.At the interview you only furnish documents that are asked for.I was asked for my bank statement here (which reflected the whole family financial situation) and wasnt asked to give any AOS even the letter that my host wrote wasnt also asked for but questions about my host were asked like, what he does, where are we going to stay and what will you be doing when in the US?
I would just recommend you to talk to your host and if he is ready to sign you the AOS then fine but if he is not ready then try to explore other avenues as I did.You have to start immediately because that is the most important document that might surely give you headache if you are not in the position of raising up your own bank statement.I hope this helps.
cheers