affidavit of support, when? also sponsor question

[starlisle 0]

When do I send the affidavit of support in? Is it with the i129f or to the meeting with the consulate (embassy)? Seems a lot of people sends it in with the I129F but it isnt necessary, whats the smart thing to do?

Also my fiance earns enough money but he has only had that job for 5 months and yet not filed for paying taxes, will he have to file for paying taxes asap?

Also, he cant be my sponsor when he doesnt have any papers from IRS right? As he only had that job for 5 months and before that he was paid very little by his dad so he couldnt pay any taxes on such little money (like 150-200 a week or something).

So that means we have to use a co-sponsor right? How much money in USD does the sponsor need to earn and what documents do we submit with this?

Also is there anything I will have to think about when the co-sponsor we have in mind has a four person household (his wife, and two children whereas my fiance is one of them) but his wife doesn't have any income but his two children has, do we have to provide their income papers too or only the co-sponsor?

And we are also filing for K2 for my child, will the co-sponsor need to earn more money then? If yes, how much?

Help is highly appreciated.