Walter would be polite, respectful and straight forward in any dealings he would have with Ned, if he wanted to ask about Muggle things he doesn't know much about, he would likely ask Ned or somebody in his department for information when required. I can see something like that happening in the past, so I think Walter would seem a decent fellow in Ned's eyes, at least he'll know the guy has a solid work ethic and to his knowledge nothing scandalous in his past.

I could have Walter seek Ned out to ask about Muggle creatures or technology that could cause the sort of injuries to the giant squid and/or take out a fishing boat on the Black Lake. It would give them something to talk about even if nothing relavent is revealed. For more information about the Black Lake Monster plot, see the following Daily Prophet articles:

Mysterious Flotsam Near Black Lake
Mysterious Injury to Giant Squid
Mysterious Monster in Black Lake
More Mystery in the Black Lake

Nobody knows what it is yet, and unlikely to be a muggle creature, but still would make a good thread topic. If interested I can start it up, if not, I'm sure we can figure out some other way to get them to thread.

For the prospective husband, we can have them talk about it, but till Ned's daughters are PC's probably best to wait on that .

Edgar is pretty careful about those he deals with as Leon, he does try to keep both halves of his life separate. (I'm assuming none of Ned's children or siblings are PC's as yet.) In either case, Edgar's pretty careful and won't make any assumptions. If he's not disguised as Leon he would deny any knowledge of knowing a person who he met as Leon and vise versa . That said, what happens in the future can end up outing him anyway.