Great ideas, I'm also looking to do this, I just wrapped up lmop and bought red hand of doom. One question I have is about space. The horde can get from phandalin to neverwinter in just a couple days, that might make the time-line a little shorter than in the original.
An old or older gold dragon is surrounded by an aura of fire. All creatures within 5 feet of the dragon take 1d6 points of fire damage at the beginning of the dragon’s turn. An ancient gold dragon’s aura extends to 10 feet. A great wyrm’s damage increases to 2d6. The dragon can activate or suppress this aura as a free action. Luck (Sp)