Probably more than half, honestly. But the stuff that's good? That stuff will be better than 95% of anything DC ever published.
I expect DC and Marvel to keep their hands off each other's toys, if and when they begin to hit the domain.
With Cap, my limited and likely flawed understanding is that he could be in the present day. Being set in modern times is too broad and vague a concept for copyright to lock down. Copyright protects specific stories, not general concepts. But how Steve gets to the present day, that story (from the 60's I guess?) would be protected and DC couldn't have him frozen in ice for decades. They'd have to throw him into the future via time machine, or just have him live a really long life or something.
And yes Bucky could grow up. That, again, is too vague and broad a concept for copyright to cover (again, assuming my limited knowledge of copyright law is correct). You couldn't do the Winter Soldier stuff of course, but Bucky could grow up.