Okay, let me talk to you about the instinctual sucking reflex. Your infant NEEDS to suck. I mean that too. This isn't about milk. This is about needing to suck. They even do it in the womb - sonograms see them sucking their thumbs in the womb.
I chose pacifiers over allowing my babies to suck their thumbs because I wanted the ability to take the pacifier away. It's really hard to take a thumb away, and I watched two of my nieces suck their thumbs all the way up to kindergarten. (They also put a finger up one nostril at the same time they sucked their thumbs - yuck.)
Your baby is helping YOU set his feeding schedule. It is okay to feed him 3-4 ounces every 3 hours. Do not feed a bottle on demand. If you were nursing it would be different, but you aren't.
My younger son was calm like yours (the opposite of my older son!) But they both scheduled like your son is doing. My babies were NEVER fat. And your son won't be either.
Offer him a 4 ounce bottle every 3 hours. Burp him enough so that he doesn't have gas. He might not take the entire 4 ounces and that's okay. In between feedings, offer him a paci when he fusses or moves his mouth. LET him sate his sucking instinct. It's important. He needs it.
Just so that you know for when he is older, my ped told me that between 4 and 5 months old, the sucking instinct dissipates, and then sucking after that becomes HABIT. I weaned my children from their pacifiers betwen 4 and 5 months. I never had to worry about bucked teeth, them WALKING AROUND with paci's in their mouths (I hate that - the paci's get dirty) and I didn't have to worry about them trying to talk with a pacifier sticking in their mouths which I also hate. But by using a paci in the first few months, I didn't have to worry about having a thumb sucker.
Do NOT deny your baby an outlet to suck. He needs it. Just don't substitute milk for sucking. The 3 to 4 ounces every 3 hours is just fine.