I think Total household size 3 is right, which sum up 1,2 and 4.
Here is the 2003 Poverty guidelines chart, I think we could base on this chart.
http://www.ed.gov/about/offices/list/ope/trio/incomelevels.html
Did you get reciept on the day you hand in I-130 or you file all the forms in the same time?
thank you and good luck