About to be a parent and the main conclusion I've come to is that being consistently reliable, caring and responsive to any distress the baby has in the first 6-9 months is number one more important thing to keep in mind. Those physical health things are either obvious or hardly matter but making a kid who grows up to experience a lifetime of emotional suffering due to poor attachment styles or mental health problems is extremely common and bad. The world is filled with these walking wounded who can't function well, can't form stable relationships, commit suicide, become drug abusers, etc. Far more common than SIDS or choking to death.

I'm curious, does your conclusion preclude sleep training, which frequently involves some amount of "crying it out"?

Yes, it precludes it in that early age range. I was taught this in parenting class and read it in a library book. I've never heard anyone advocating for leaving your baby alone to cry when it's that young except as a "least bad" choice if the parent is losing control of themselves and might shake the baby in frustration/anger. It's probably different when they're older but I'm not up to that yet.

To be honest, the baby’s most important resource is the parents themselves. Sunlight and fresh air is good for that at least. Similarly, let somebody else take care of your baby every now and then so you can connect with your partner!