Not only that but everyone in my area who has a house my size have 3 units as well. ?
And are all of those houses the same size as yours foamed. And are they all sized the same they want to do yours. If so. Ask them how their indoor humidity is, and if they have to use a dehumidifier to be comfortable.
spray foam in the walls isn't the way I'd go in my hot humid climate.
rigid foam sheathing would be more cost effective.
the foam sealed unvented attic is worth the investment.
sizing hvac system, designing duct lay out & mastic seal will be less than foam spraying
walls & serve you much better.
in texas the saying is bigger is better...but it doesn't apply to hvac.
too much a/c & you'll have high relative humidity.
and will be uncomfortable in your home.
people in my similar climate have learned this the hard way.
I'd suggest that you not go that route.
another thing to think about is a whole house dehumidification system.
best of luck.
The cure of the part should not be attempted without the cure of the whole. ~Plato