Hello and welcome!
The VC route has an unavoidable road-route for the first several KM, but there is an alternate into the first villages that goes just off the side and by the river (if you use the Wise Pilgrim app on a phone, you will be able to have a live map to locate that). After Valcarlos itself (which has so much to offer as a lovely rest-stop in a fully functional village of resources, including an albergue should you wish to break up your day), much of the rest of the walk is via the woods, by the river, and up-up-up. and you will join up with the Napoleon route at the small church and monument to Roland. After that you descend together as one approach into Roncesvalles.
Heading out n the 28th of March, could be wet/cool/snowy... who knows! so make sure you get nice and warm in Valcarlos!
As to signage... yes, it is well signed, and the foot trail through the forest is easy to follow. Personally, I prefer the sheltered forest to the exposed Napoleon route at any point....
And you will still have gorgeous views.
Buen Camino!