I mean if you did the Star Forge idea, would you have Phasma lower the shields and give them the map? Or just have no planetary shields?
Like I said, I think making Starkiller a Star Forge alone would still be a worthy idea to try and implement. I would at least see if it is possible to have the third act still focus on the McGuffin if possible too though.
My edit will attempt to have Rey find Luke without a physical map - she will have a vision of it when she touches the lightsaber. So if it is somehow possible to remove the shield idea, Phasma could become a stronger villain by denying Han and Finn everything they want and sounding the alarm.
Rewatching the Resistance briefing scene, every other line mentions either a shield or a weapon of some kind, so for that scene to work Starkiller would need to have at least one of those capabilities.