Hi hun
Congratulations on your gorgeous bub.
First of all, your bbs will be hard & sore for a bit, coz your milk has just come in. They will be over compensating to make sure there is enough to feed your bub.
Expressing for comfort is a good idea, but try not to express til completely empty. The more you empty the more they will make. Supply = demand. What is taken will be replaced.

When he comes off coughing, it's probably coz your milk is letting down. It'll be colostrum for a few sucks, then let down will happen & for a few seconds it'll be hard & fast, but then it'll settle again. You might even be able to feel it.

With your attatchment, keep persevering. It does take a while to get the hang of it. It'll be good, then bad, then good again. If you've attatched wrong just once & there was some damage done, it will hurt til it has healed. Usually a few days.
Just keep a close eye on it at every feed & you'll have the hang of it in no time Reattatch as many times as you need to.

ETA - 1.5 to 2 hours is perfectly normal at this age