Hmmm, he seems pretty hungry!!!! Is that his normal formula intake? What a healthy guy! IMHO, he sounds like he's ready to start solids, but whether or not you DO is a completely different story. If you'd prefer to hold off until 6 mo, there's nothing wrong with that...it isn't a law that you have to start solids once he shows signs of readiness. Some things to think about...the farting around during feeding is an age thing. He's noticing that there's a world around him that keeps moving while he's being forced to sit still and take a bottle. He could do the exact same thing once you start solids, or not. Who knows? Solids on a 3 hr EASY can be a PITA because there isn't much awake time for feeding. Solids may or may not help fill him up enough to shift to 4 hr EASY (I'd guess they would, though). Whenever you do start, I'd advise starting with something other than cereal if you can because of his constipation issues. Pears are a great first food.
Keep in mind that if you do start now and it doesn't seem to be working out, you can always stop and give it a go another time! Keep us posted and let us know what you decide and how it goes!