But you can pump between feedings and start to build a stash in the freezer. If he's sleeping pretty well at night you can pump then too. That way he'll get the good stuff that's not going to upset his system.
I'm with your hubby on soy for boys (and girls too for that matter) but sometimes it's necessary. There are the other type of hypoallergenic formulas. I was just reading an article on cnn.com maybe that they seem to be digested more like breastmilk but they are the priciest.
You can't rely on solids to make up the difference if you are out and about. Solids are only for practice in the entire first year. Breastmilk or formula is primary. Solids shouldn't even be started until at least 6 months as baby still has an "open gut". 6 months is just the starting guideline. My ebf baby wouldn't touch solids till she was almost 9 months old. Given your family history of food allergy issues you def want to hold off on solids.