I’m at Level 108 now and just finished that KiMa’s tedious mental puzzle inside The Nucleus. I also added The Slog to my large-size settlements; only 27 peeps, but I’ll be moving Curie and Danse to other settlements soon and then build-up the regular settlers.
I’ve also been increasing the number of provisioners I have running caravans through the northern region of the game. Currently, all settlements average around four caravans. In my early FO4 games I really disliked the idea of running provisioners, but now there seems to be proof that the more caravans you have in a region, the better the security is. The security improvement is also a result of having a large numbers of minutemen manning checkpoints near the active settlements.

These are my current provisioner routes in the northern half of the Commonwealth.
Currently I have five large settlements, six small settlements and one safe house, for 300 settlers, so I’m still not fully built out. I’ve avoided several settlements like Greentop Nursery, because it is very difficult to build on and the settlers seem so unwilling to do their jobs; what is that all about? I’ve also avoided Finch Farm, Taffington and others, but I may add a lot more when I complete all the DLCs. I am looking forward to building a large settlement at Kingsport Lighthouse, but first I want to create a cool place for Old Longfellow (Luv this old guy).
Anyway, I still have a lot of work to do before I’m ready to put Fallout 4 on the shelf. I’ve ordered an external drive for Xbox and plan to back this iteration of the game up, before I begin messing around with Sim-Settlements. This game can be a lot of work, but when you complete a major questline or build another large settlement, it can be very rewarding. More to come…
OH, OH, OH! Before I forget.
I figured out a way to avoid killing lost characters (NPCs that get stuck in inaccessible places), just “Move” them (using Settlement Management Menu) to an unused settlement. The odds are, the NPC will never actually make it to the new settlement, but at least you can now recruit and assign a new NPC to their job.