Juro's comments are right on. I'll just add a few additional comments . . .
I've been using dyed Golden Pheasant flank feathers for spey hackle on smaller flies recently and am loving them. And Golden Pheasant flank works really well for Lady Carolines.
Brittle stems are something you can't really do anything about (except by avoiding tying with them), but you can alleviate some of the stiffness of hackles by steaming them prior to tying. I just learned this trick in the last couple months - the steam softens the stem and allows you to wrap the hackle with more control. I've found this allows me to get that flowing, slightly curved positioning on the fly more consistently.
The final ingredient is *practice* - you learn to tie these flies by Doing It! I wish I could post a pic of my first attempts (some came out looking like Mohawks) to emphasize this. And others who are much proficient tiers than I tell similar stories.