LOL ... I doubt many of your friends will be scouring our site for your "secrets" - and I doubt that if any of us got up to the area around where you live we would run into them.
I do like the idea of the mousse instead of pudding. And, it - along with the jam, shouldn't be a problem to assemble the night before.
The main reason for holding off on the whipped cream until near serving time is because it doesn't hold up well.
Really trying to read between the lines here on the grape juice ... slice of cake brushed with grape juice instead of a liquor? That should work and not make the cake any soggier than if you used a liquor.