I just want to be prepared if and when I have another baby and try to do better.
My advice below is based on the statement above and in no way a suggestion that you 'failed' or did anything wrong with your son - you didn't and you did an amazing job expressing.
I've breastfed 2 kids, 1 vaginal and 1 c section, and I do have some breastfeeding peer support training, but I'm not an expert. I didn't have skin to skin after either birth.
Milk takes 3-5 days to "come in" but can take up to a week. Colostrum in those days is sufficient, they only need tiny amounts but frequently, every 90minutes or so. Breastfed babies fuss. They get frustrated, they bang their tiny little fists on your breast, they scream and thrash and throw their heads around. They get angry at your boobs and at times it feels like they think you are poisoning them. BUT THIS IS NORMAL.And good! And you've got to let them do it. All that behaviour triggers a response in you to make more milk. I often hear new mums say things like "he's not getting enough from me" or "he's clearly starving" etc and they give formula, and the behaviour stops, and this reinforces their belief that they aren't producing enough milk. But by understanding that the behaviour is necessary for you as mum to produce more milk it reduces the anxiety.
Stick baby on the breast every time they open their mouth. Literally. Newborns feeding cues are super subtle, thrusting of tongue, a yawn, a stretch, turning the head. All early feeding cues. By responding to the early feeding cues it reduces the risk of baby being too upset to latch properly.
You could consider prenatal expressing for colostrum, so if you can't feed straight after birth baby can be given colostrum. Also, consider cup feeding if you do give formula. There's lots of great YouTube videos on it.
If baby is sleepy. Wake them up- strip them off, tickle their feet. Make sure they actively feed for at least 10 minutes every 90 minutes. Once they regain birth weight you can stop that and let them set their own feed schedule, but no more than 3 hours between feeds until feeding is established (usually 6-12 weeks but can be longer).
Bad latches, tongue tie etc, are also issues but I won't go in to that now.