One of the things I really like about the canon history of The North of Faerûn is that there were many dwarven and elven kingdoms that have fallen to orc hordes and other disasters. This provides a logical reason for the existence of dungeons particularly for 3E's Forge of Fury.
There's no real need for any additional background for this adventure: it basically fits anywhere in the Nether Mountains or in any of the other hills or mountains of the Silver Marches largely "as is". It's an entirely self-contained site-based adventure that involves killing things and taking their stuff. Other than stat block and magic item conversions, I think this one's good to go.
Also, so far I haven't mentioned the presence of any dragons... but Forge of Fury fixes that rather nicely:
One black dragon ready for action.
So far my ideas don't feel like much of a sandbox but I do rather like the progression from B1 In Search of the Unknown to B2 Keep on the Borderlands to Forge of Fury. With three solid site-based adventures I've got a fairly solid foundation on which to lay the more sandbox-like elements... and places to point the PCs when the sandbox is not scratching the players' collective gaming itch.