I'm so sorry about your sweet Runner Duck. They are my favorite type. At about 2 weeks old, I started my babies on grit, and I mashed up some over ripe bananas with water, as a treat. They loved them. Whenever we have bananas with black spots, I won't eat them and our Indian Runner Ducks get so...
I just found your topic and am excited to see how your babies progress. I got show ducks this Fall but am waiting till the Spring to incubate ducklings. It's too cold here to have baby ducklings right now.
If you use hardware cloth, instead of chicken wire, it is fine. That's what my Call Duck cages are made of and I never have foot problems. My nesting box is solid wood bottom, but some people put wire in the bottom of that too.