You should be able to determine funding requirements with the help of the Berkeley International Office. If I were to ballpark it, and as you note the figures can vary significantly, I would be thinking @$1800/month for the J-1, $1000/month for spouse, and $500/month for the child, meaning that there would be a need to demonstrate financial certification in the amount of at least $3300/month for the entire duration of your program; but I don't have your local information and you do need to verify the numbers for your location.
The J2 visa is for qualified dependents, and there is no "minimum length of marriage" requirement. There are many factors that can affect how quickly a DS-2019 and the J2 application process are completed. Once a J2 is approved the holder can travel inside and outside of the U.S.

