You wouldn't need to come up with the full amount all at once. You would be asked to pay a certain amount every month in arrears until the arrears are paid. Ex could easily return that money if they wish (but, as I said, I doubt that they would really do this).
You can probably find the answer to your question elsewhere on this site - try searching for it since it has been answered several times. I don't remember, but it's something like 25% of income for one child and 40-50% for two or more (but I could be way off, so do a search and you'll probably find it. There are also a lot of good articles on the main page).
You can probably find the answer to your question elsewhere on this site - try searching for it since it has been answered several times. I don't remember, but it's something like 25% of income for one child and 40-50% for two or more (but I could be way off, so do a search and you'll probably find it. There are also a lot of good articles on the main page).