2. When showing a cartoon of DNA the ribose ring in the backbone is
always there no matter which setting you choose. How can I make the
phosphates and the ribose rings show as a backbone cartoon "tube" and
keep just the bases as filled sticks with rinngs?
load nuc_acid.pdb
as cartoon
set cartoon_ring_mode, 3
set cartoon_ring_finder, 2

3. Rings on DNA and RNA can be filled, in cartoon mode. But I can't get
the rings to fill in on selected amino acids (H, W, Y, F) in a protein
of that same file. Is there a fill amino acid ring setting?

load $TUT/1hpv.pdb

as cartoon

set cartoon_ring_finger, 4