Soft opening "should" be daily... and march is when they will be having Employee Preview, Ellen Preview, & AP preview... so you should have no issues with being able to venture into the new land, unless it is "closed" due to one or the previews going on or some other reason.
As for the park maps... I wouldn't expect new ones until April either. I mean, come on.. they couldn't even be bothered to add it to the map with a "coming soon" or "opening April 7th" in the area it is supposed to be. Sure the map has an image with the opening date, but that's "meh".
I'm also curious about FJ... if it is as toned down & not properly aligned as Orlando, or if it is actually thrilling like it was designed to be. Oh and dementors... curious about the dementor finale.