When I bought my setup at Appomatox River Co here in
VA, the method used to determine proper length of a
paddle was for me to stand straight, lift up my arm next
to a paddle and bend my fingers over it. If I could do so
at the middle finger joint, it was perfect.
With wider kayaks today, this doesn't always work perfectly.
You don't want to be scraping the sides, esp. if you have
short arms. A longer paddle will help.
And as for bright paddles being a waste of time, that is an
entirely subjective statement. A flag is great, but if you're
standing up and not being recognized, having something
else to flail could be useful since you're above the flag
visibility line of sight. Pick your tool...LOL.
My paddles are white. I like black, too. In fact, I'm rarely
using a paddle given I motor everywhere. And those who
use pedal boats are not using paddles. So yeah, a flag first
for visibility, but if a paddle helps you feel safer there,
then go for a hi-vis color. If they're not seeing you, blow
your horn. You have one, right?