Torben:
 the peel n stick is a good idea, but do not cut out for clips , instead use a continious nail strip standing seam.
3/4" R-max is totally unecessary

the 4" could be problematic on a roof for sound, 6" is far superior

Yes, Chris, there are A LOT of things I wish I had done differently. Right about now is where you can say "I told you so."    :)

But what do you think about the 30 lb. felt versus the self-adhering bituminous underlayment? I like JeffD's idea if it will make a big difference. Of course I have to look into price.

The majority of the living space of the house is under a ceiling which is under a conditioned attic. So regarding my 4 inch roof, I don't think sound would really be an issue in those areas.

However there are two 2nd floor bedrooms which are directly underneath the roof with no attic in between. I will definitely fur out the ceiling there, and maybe add some rockwool?

Jelly;

I like the peel-n-stick better for several reasons, cost is about 40 cents/sq. ft.

you will be OK with the ceiling drops, but definitely needs furred in other areas

So wouldn't the seam tape and buckets of elastomeric sealant that I bought be redundant if I used peel-n-stick?

Jelly,

Yes it would be redundant.

 elastomeric serves no purpose, if you seal the joints with tape the metal is already impervious to water, you are looking for sound deadening that the bitumious peel-n-stick will provide