I went through the exact same thing except my son's night-time sleep stretches were shorter than 4 hours.
Don't mix cereal in the bottle, it's an old remedy that works for a few kids but has no scientific basis when studied - it just happens to work for some, mostly because their digestive systems aren't ready to handle it so it just sits in their stomaches without being digested (does that really sound like a good option?).
A baby will ALWAYS take more from a bottle, whether or not he or she needs it. Your body may be making almost that much and you just don't realize it. Or, your baby gets what he needs at the time and is just fine. If you are worried about the amount he is really getting from you, bring him to support group at Community Hospital (PM me for days and times). You can weigh him before and after feeding him so you know just how much he takes. As long as he's peeing and pooping and gaining weight, you really shouldn't worry and don't need to supplement. There are things you can do to beef up your supply if you want to do that as well.
My son woke every 3 hours for the first 6 months. The truth is, in breastfed babies, as long as they aren't getting up to play only to eat, they are considered to be sleeping through the night. Breast milk is SOOOOOOOO good for them, partly because it's so easy to digest, which means it doesn't just sit there in his stomach making him feel full when he's not getting as much nutrition like from formula.
When he starts to show signs of wanting to eat (watching your every move at the dinner table, reaching for your plate, pretending to chew) start with regular food, not cereal. This will get more calories in him and help him sleep longer stretches. There's no reason to start before he shows signs of being ready (and yes, it could be later than 6 months, wait for him, don't force it). Start with things like avacado, mashed banana, and sweet potatoes. They are all very high in nutrients and calories. Cereal was developed to "teach a baby too young to eat, how to swallow against the tongue thrust reflex". It's iron fortified for formula feds who don't get the good iron from mama and can make breastfeds pretty constipated.
As for naps, here's what worked for us (Eli was taking 30 minute naps a few times a day and crying most of the rest of the time):
With information from a combination of books (PM me if you want titles) I learned to better recognise his sleep cues early on. I had gotten so used to him nursing and then sleeping that I was missing the signs that he was tired even when he wasn't nursing. I put him in the cradle (or car seat because of his reflux) and covered it with dark fabric or a blanket. I turned on a fan for white noise. He quickly fell in to a much better sleep pattern and developed a regular schedule within a few weeks. The best I found was
Eat
Play
Sleep
So when he woke up, I would immediately feed him. Then he'd have his awake time and as soon as he got a bit fussy, rubbed his eyes, or yawned, I'd put him back down.
I hope that is helpful.