Cedar Shake Shingle Siding Installation question???
 

I'm somewhat familiar with isntalling cedar shingle siding, however
there's one or two aspects that I've never quite been able to get good
clear information about.

#1 On my cedar shake/shingle house, the shingles just butt right up
to the sides of such things as door trim/ window trim and corner
boards. There are no flashings and there is no caulk. I understand
that caulk is not practical in this application because cedars shakes
expand/contract so much. But is there some flashing that should be
used? I was told by a roofer/sider guy that its not necessary because
there's tar paper behind the shingles? I'm wondering because I am
about the re-side another house with shakes, and was hoping to find out
if there is a flashing for these situations...and if so how is it used?

#2--If I am residing a house with shingles....should I put the trime
around the windows and doors on first? Or should I wait and put them
on over the shingls?