This seems like a good idea. The Goblins could be seeded to foreshadow the Hobgoblins. Are the goblins advanced scouts? Fleeing the advance of the hobgoblins?Lost Mines of Phandelver (starter box) would be easy to drop into the Elsir Vale or just outside of it. That's what I am planning on doing. That would get characters to level 5. Then throw in something to transition from LMoP to RHoD and get the characters another level and you're good.