Do you know if this is the mission where you have to branch out towards a faction?
I'm trying to find a point in my saves where the story is right in the middle, so I can replay each side from there and get all the faction achievements instead of starting completely over.
Yeah make your save point here for achievements. Molecular Level seems to have a couple follow up missions specific to each faction that all lead to one mission later, but those follow up missions have achievements. But for example, the Minute Men do not have anymore achievements past Old Guns which can be done before Molecular Level. So finishing the game with Minute Men can be done off of a save that's still way later on while chosing a different faction for Molecular Level.
I'd honestly just refer everyone to ps3trophies. Fallout 4 Trophy Guide.
For achievement purposes you actually only have to finish the game once. So deciding where to save by that guide is purely for achievement purposes (miss-able missions). Mass Fusion is the first mission I played that actually caused me to fail other faction missions, so as far as getting endings its fine to do anything up until there.