I am always happy to see that someone else has fallen under the intriguing spell of runner ducks!
And, I applaud you for your approach to managing your property. Best wishes with adding to your food forest!
I don't know what your ideal ratio is; when I got my first runner ducklings, I ended up with three drakes and one hen.
The boys, maybe because they grew up together, didn't attack or hurt each other. I worried that the lone girl would be over-bred, so I added more females. But, honestly, she seemed a bit jealous of the new girls; Quinn would walk up to a drake that was with trying to mate with another girl and would "flirt" to get his attention.
Welcome to BYC; hope to hear more from you!