I know you've said before that your Lo doesn't spit up so you don't suspect reflux but have you considered silent reflux? My DS had silent reflux, barley any spit up although when he got to his worst he would bring up milk 3hrs after a feed - but the symptoms are perhaps not so obvious. It's just that you do have a lot of NWs and disturbance there which sounds like possible reflux to me. When they are in pain it's pretty much impossible to do anything other than hold them so they know they are not alone. I had that many a night until my DS' reflux was under control with meds.
Let me try to answer your questions:
I have read read the post on pu/pd, and following Henry's dad's thread, but have a few questions myself
I need to point out that H's Dad is a thread about a LO who is around 10 months old now - the age difference is pretty big. It's great to read through other threads for ideas and tips but do take this into account. We don't really suggest PUPD for 4 month old babies. With shush/pat though you DO pick up when they are upset and you DO put down and continue shush/pat in the cot when they are ready for it.
Reflux babies don't do so well with lots of picking up and putting down, it's like shaking a soda bottle and can aggravate the reflux acid. Your LO may not have reflux...but then again, might.
1. If during a NW, and LO is awake but not crying do I leave him or would I pu/pd to get him to go back to sleep so he doesn't create a habit of waking..
Leave him if he is quiet. Stepping in too soon doesn't help with sleep training, he will call if he needs you. PUPD or shush/pat don't force your LO into sleep, they just let LO know you are there when they are upset or frustrated.
2. Pupd should be used as a last resort. If I can have him sleep by shush pat then ok to do so?
Certainly shush/pat is the first choice method. Even in H's Dad thread they have supported LO in the cot with a firm hand and patting or adapted to help LO know they are there.
3. What is considered "calm" before putting back down ? Completely quiet with no crying at all, and completely relaxed with no squirming? Or a little bit of moaning or mantra cry acceptable at pd?
It really depends on what stage your LO is at. Independent sleepers can actually grizzly and fuss because they want to be put down and left to sleep. On the other hand a LO who cannot self settle might need to be shush/patted all the way to sleep in arms and then transferred to the cot where shush/pat continues for a further 20 mins into deep sleep.
This is something you learn about your own LO and perhaps figure out through trial and error.
4. How long when baby is calm should I give before putting back down? 1min? Some time lo became quiet but 30 seconds later resumed crying again
There is no timing with shush/pat other than you keep in mind your end goal of getting LO to sleep in the cot and learning to self sooth. LOs don't always need picking up, they can be soothed in the cot but if he is kicking up a huge fuss and crying hard of course you need to pick up and calm him. Even a fully independent sleeper can have times they need to be held for long periods and a lot more help to calm down if something is bothering them (teeth, illness, reflux).
5. After pd and he begins crying is it OK to try to shush pat to sleep if he will allow it or should I continue to pupd until he is quiet upon placing back to bed and no longer fighting sleep?
Yes, use shush/pat. Even LOs who are sleep trained using PUPD need a "lesser" support in the cot either a firm hand on them or patting or verbal reassurance with a key word etc.