MinnFlyer gave you the right anwer, but he didn't tell you how. They give scale in two different units on purpose to confuse you.

3/4" = 1'

is the same as

3/4" = 12"

So divide .75 / 12 = 1/16 scale

As far as the props go, I think the .09's are too much for this plane. I would use 1/2A engines such as Norvells. Why do you want 3-blade props? Do you need shorter props for clearance or are they just for looks?