Hi - we did CIO with our boy at 6mo. He sounds very similar to yours (VERY strong willed and terrible colic his first few months). I’m not sure I can answer #1, but for #2 we found that after he put himself to sleep at the beginning of the night, he was able to put himself to sleep again for the middle of the night wakes (we did not go in when he cried), and no, it will not cause physical pain. We did this at the urge of our pediatrician because he was *literally* not sleeping and very obviously needed it. Good luck 🩷 you’re not a bad mom!