It's been a while so I'll shout it from the rooftops again: if you're going to start a new game of Fallout 4, you should install the Sim Settlements 2 mod. Not only does it make settlement building and management a much better experience, it adds a bunch of new characters, lots of quests, and an intriguing storyline.
If you're not familiar with the mod, it's a complete overhaul of the vanilla settlement building system. Instead of doing all the work yourself, you can zone your settlements for different purposes like residential, commercial, and industrial—a bit like playing a city builder—and then let your settlers take things from there. And if you do enjoy building and micromanaging, you can still build as much stuff as you want alongside the mod's overhauled system. It's the best of both worlds.
Basically, the mod does what Preston Garvey should have done: it makes settlement building awesome and interesting instead of just a chore.
The story of Sim Settlements 2 is broken into chapters, and the third and final chapter has just arrived. As you can see in the trailer above, the concluding chapter is all about war as the defeated Gunners return with reinforcements and some advanced new tech. To prepare for the coming conflict you'll be able to turn your settlements into proper military outposts using new building plots like armories, watchtowers, prisons, and field medic stations. You can also recruit settlers into your growing army and establish new bases pretty much anywhere you want on the map, not just in the vanilla game's preselected settlement spots.
And gosh, the settlement invasions and battles shown in the trailer look much, much bigger than the skirmishes you encounter in vanilla Fallout 4 where a half-dozen grubby raiders run into Sanctuary and start popping off their pipe-guns. This is full-scale war. I know war never changes, but modders sure make it more exciting, huh?
Just because it's the last chapter of the story doesn't mean the mod itself is over and done with: another interesting twist to Sim Settlements 2 is planned for a future update. A "prebuild system" is in the works, meaning that when you start a game the world will be seeded with randomized pre-built settlements, some friendly and some less-than. That'll give you the chance to stumble across existing settlements instead of just blank plots to build your own from scratch. That sounds cool, too.
The Sim Settlements 2 official site has everything you need to get started, including download links, installation instructions, wikis, forums, and more.