Answers to your questions are mostly yes.
It is NOT a picky car.
Red line is identifiable when the car won't go any faster in the
gear you are in.
Shifting too soon may save a little gas but really doesn't help
anything else much.

Any good-quality oil, 10W-30 is fine unless oil consumption is a problem,
then you can use thicker.

I use NGK plugs - BP6HS or if fouling becomes a problem, BP5HS.

Gas mileage depends on how you drive. Constant high speed should get
you at least 25 mpg. I've gotten as high as 33 in a wagon on a long
fast trip with overdrive.
Congratulations on getting a fine piece o' arn!
--
George Downs Bartlesville, Oklahoma