For a lot of this stuff there is no right or wrong, you have to find out what works for you. Cadence is very personal, for example.
Some people like to stand a lot, others don't. I rode along with a local pro for about 10-12 miles on a slight grade and he never sat down! I have also seen guys climb for miles without sitting.
I have pictures of myself from 17-18 years ago when I was more flexible and I could never get a flat back. I look like I'm pretty upright when I'm in the drops.