First of all, dont panic and leave PLENTY of time. it does take twice as long as normal, but you get used to it after the first few times!
It really does help to have him in a stroller, just for ease of having hands free for ticketing, ids out etc.... they will make you take the baby out of stroller, sling etc through the security anyway and of course if you are going through hartsfield you pretty much have to strip down anyway!! its much easier with baby in his car seat, then you can get you sorted, take the stroller down, then take him out before you go through security.
Once you get to the gate the baggage people will gate check your car seat and stroller, just take him out and leave them by the door. They will be waiting when you get off. If its a long flight, check the seating availablity, if there is an empty seat next to you, ask if you take in the baby seat - we did this a few times without having to pay for a seat. That way hes next to you without you having to hold him the whole flight. And if the seats do fill up, they will still gate check your seat for you!
Make sure you board first, even if they dont say families, get in line with the first and business class people. Try and get bulkhead seating or right at the back. theres more room and its usually by the kitchen area (and restrooms) which is a great place to take a crying baby as its a little more private. usually the staff dont mind if you just ask them. ive found that sometimes they will actually want a cuddle! Dont be afraid to ask them anything either. Dont worry if other passengers are rude, just say "Im doing the best i can", theres usually no answer to that!. Our daughter actually always fell asleep pretty quickly as the motion lulls them. But time your feeding for when the plane is taking off - the sucking motion helps with the air pressure, so it doesnt hurt his ears and after a good feed he should fall asleep! We've done 4 international flights and 4 domestic with our daughter from just a couple of months old and even though i do get stressed, as long as you take your time and ask for help if yu need to, it will be fine. Good luck!.