You pretty much answered it already. The pekings need to go . It is never good to put any domestic breeds in with any wild species. They are bullies and will stress wild ducks. Any stress results in no production. Also you need a lot of cover in the pen to make them feel secure and safe.
Without that and will aggressive pen mates, these kind of ducks will never reproduce.
Also mandarins are fairly common on not breeding til they are 2 years old. Which may be part of it .
Yes they you start early spring for you .
Yes they molt mild summer , so that's normal.
If the male was ratty looking he most likely wasn't kept well where you got him from , sign of more stress. Also sounds like you got him at peak breeding season. That's more stress. Moving to a new home right at breeding time will shut them down too.
Make sure they have swimming water. I bet since he was in bad condition , he did t .
Yes get the domestics out and you can add wood ducks.
These two species are generally the most high strung , nervous of all wild ducks though . So make the pen comfortable and secure to them , or they will never breed for you
Hope that helped