Jen
Online are childsupport calculators that the courts use to determine how much support you can get. I live in Ohio, I'm not sure where you are, but if you are in the States, perhaps you could call a local social service agency -- even the WIC people could point you in the right direction -- in order to find the calculator that your court would use. What you do in punch in your STBX's yearly income, your yearly income, and how many minor children you have, and it will calculate how much child support you are likely to get.
I wouldn't let the house go into foreclosure if I were you, because that would hurt your credit. If you think you'll be late with some payments, the best thing to do would be to contact the mortgage company right away, as I've heard they will be happy to work with you over a certain amount of time in order to avoid foreclosure.
But possibly, if you decide to keep your home, you could refinance at a lower interest rate, and then sell when you are ready to, rather than be rushed about it right now.
Jean