Take a deep breath. You have a good attorney, H has a fool for an attorney (himself) and if your offer is reasonable according to the laws of your state, the judge will not be impressed with him if he is not coming back with a reasonable counter offer.
During negotiations, you might remind him gently that two households are always more expensive than one, that everybody's standard of living goes down in a divorce, that you are not asking for anything that the law doesn't allow. Also figure out what you are willing to "give" him in the negotiations; you want to try to make it a "win-win" situation where he can at least come away thinking "well, at least I got XY or Z". Is there anything small or stupid that you can give him if he needs a "win"?
Also, stay STRICTLY away from any emotional discussions; this is about the business of divorce, do not let him lure you into any emotional talk.
There are formulas for child support, alimony, dividing retirement funds etc. Your attorney can give him a pretty good idea of what the court would decide. If he still insists on going to court, I'm betting you'll do just as well with the judge as you will with mediation. I know it will be frustrating not to be done with it, but I still think you'll come out all right in the end.
