Sounds like great progress
1. Is it best to go cold turkey and use this (patting in crib) for naps and bedtime or should I use this approach more gradually. Maybe start with first nap only?
I'd try on every nap but aiming for one per day is fine too, just make it the same one every day so it is habit forming
2. I suspect baby is about to start teething very soon. Should I hold off on this approach until teething is done?
There's no need to hold off but just be aware that if LO is in pain some naps/nights will be harder than others, go gently, if he needs more help at times that's fine, if you can put him down drowsy then great
3.With shh/pat, should I still wait until baby is drowsy to start or should baby be put down wide awake?
shush/pat until drowsy in arms, continue to shush/pat in crib. If possible stop just before the eyes shut, this might not always be possible but it's your aim. When it's consistently possible then reduce how much you shush/pat in the crib.
4. How long will it take for me to just put baby in crib and have him fall asleep on his own after using shh/pat?
All depends on the individual LO and also on your approach. To keep moving forward with this I would recommend staying alert to LOs signals. It is sometimes easy to get carried away with the shush/pat and get caught up in the rhythm of it yourself, if you do this you may shush/pat much longer than necessary and be teachign LO that you will always do it all the way to sleep and even throughout sleep. You aim to do as much as needed and no more, gradually reducing a little at a time.
hth