Yes they wanted to do PP from the start and there have been hints to PP since the start; the library clock for instance moved to 8:15 which is both a LOST and PP reference.
The sign isn’t magical, hence why it’s not in Rumple’s shop. There are many things that aren’t in his shop. His shop has items HE had in FTL, like the puppets, or other magical items. Just because it’s not in Gold’s shop doesn’t confirm that this is Snow’s house. There is no definitive proof. I’m not saying it’s not Snow’s, I’m just saying that we don’t know for 100% certain that it is. It’s just a place with a fence and tree and someone put a fairy sign up. It’s like having a gnome or flamingo in your yard. If there is greater significance then awesome but it’s far more likely that it’s just a decoration that the set designers put in because it’s a show about fairy tales.
I don’t know what you mean about the Nanny. Joanna was Snow’s nanny, but she’s a real character, not a stragitically placed symbol. And the Snow White is not the plot of the whole show. The plot of the whole show is fairy tales. Snow White was the jumping off point but it has diverged wildly since then. The family is main point.