In the US, he would owe child support based on the difference between his income and yours - and yes, if 50:50 custody was arranged, then he would not owe child support. But since he's not even in the same country right now, he obviously can't have 50% custody. In our country, adolescents the ages of yours would also have a say in which parent they wanted to live with.
As for spousal support - if he makes significantly more than you do, shouldn't he owe you spousal support as well? This helps to make up for the difference in income between a parent (him) who was able to pursue their career to the fullest extent, and a parent who worked less, got fewer promotions, or pursued a less lucrative career in order to run the household and care for the children. If your incomes are similar, then this would not be an option.
I'd run all such discussions through your attorney. Walkaway fathers are almost always perturbed that they actually have to pay for the privilege of nearly abandoning their family.
Be prepared, though - if he would make much less money in your current country, he might try to come home and work there just so his income looks worse so that he can then get a divorce decree that orders him to pay less. Don't fall for any of the manipulation, let your attorney handle these things. Even if you are doing mediation, you may need your own private attorney to handle communications and look after your interests.
