Adding wall insulation to an existing home.

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I agree with others an energy audit is in order. You need to know where the leaks are and fix them. In my house with brick exterior i discovered a slot cut into the outside sheeting when i remodeled a bathroom. I assume the slot was cut to pass something through the wall. Due to a roof leak I had to replace the drywall in a corner of one bedroom. I discovered a whole section of the sheeting missing. The brick and mortar were plainly visible.
I blew insulation into my walls and altough I have seen good distribution in the 2d example above i cant say it was that good in all the walls.
On foam a concern is outgassing. Also two part foam is active fot a period of time then the activity stops. At this point it looses some of its insulation value. Im not sure how it handles normal expansion and contraction. My father had it done in one home he owned with plaster walls. Wall bulging is an issue hower short of a fire break i doubt anything else in a wall would stop it.
My guess is windows and doors are your biggest source of leakage. I insulated the walls and the attic in my home but until i replaced the windows and doors I didnt see the benefit. So stop the leaks in conjunction with insulation is what worked for me. As othrrs have mentioned you may already have the insulation.
I would find a good independent contractor and take advantage of the window sales that occur every spring at the big box stores and replace them all if the audit determines that is your problem.
I know when I got my windows I didnt spend money on higher R exotic gasses because tbe returns in my opinion were not worth it. You probably should consider blocking the UV.
I put Pella aluminum clad in my house and have been very pleased with them.
Id do the ac balancing last if its needed just because youre going to tear out drywall.

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I agree with others an energy audit is in order. You need to know where the leaks are and fix them. In my house with brick exterior i discovered a slot cut into the outside sheeting when i remodeled a bathroom. I assume the slot was cut to pass something through the wall. Due to a roof leak I had to replace the drywall in a corner of one bedroom. I discovered a whole section of the sheeting missing. The brick and mortar were plainly visible.
I blew insulation into my walls and altough I have seen good distribution in the 2d example above i cant say it was that good in all the walls.
On foam a concern is outgassing. Also two part foam is active fot a period of time then the activity stops. At this point it looses some of its insulation value. Im not sure how it handles normal expansion and contraction. My father had it done in one home he owned with plaster walls. Wall bulging is an issue hower short of a fire break i doubt anything else in a wall would stop it.
My guess is windows and doors are your biggest source of leakage. I insulated the walls and the attic in my home but until i replaced the windows and doors I didnt see the benefit. So stop the leaks in conjunction with insulation is what worked for me. As othrrs have mentioned you may already have the insulation.
I would find a good independent contractor and take advantage of the window sales that occur every spring at the big box stores and replace them all if the audit determines that is your problem.
I know when I got my windows I didnt spend money on higher R exotic gasses because tbe returns in my opinion were not worth it. You probably should consider blocking the UV.
I put Pella aluminum clad in my house and have been very pleased with them.
Id do the ac balancing last if its needed just because youre going to tear out drywall.

I have a contractor coming next week to give me a price on fixing all the air leaks in my system and upsizing the duct to one room. But i made a replaceable grid system for my basement so I dont have to tear out a bunch of drywall.