A tip: You can carry tyres, traffic cones and some other items from outside your settlement inside your settlement area and then you can scrap them.
Anymore I just start linking supply lines as soon as I can. Even with maxed carry capacity, I don't care to bog myself down with construction supplies. I also find supply lines once linked, rarely get broken and require a new person to take it over.
I also agree with what was said about attacks being seldom, making building elaborate fortresses kinda pointless. I always just add some basic turrets, and fencing and guard stations where needed. Only place I've ever used more elaborate turrets is the Castle, to prepare for that one major attack.
The main reason I stopped playing while waiting for Far Harbor, is boredom. It's too easy once you get a few nice weapons and skills, and there's not nearly enough faction attacks.
Truth be told, I've been playing mostly Dying Light and it's The Following DLC lately. I'm playing on Nightmare this run through. There is MUCH greater chance of dying in that game than in Fallout 4, especially since the Enhanced Edition changes. Plus you lose a lot of Legend points when you do. You have to carefully plan your moves to keep them long enough to apply to a skill upgrade. And unlike Fallout 4, death is just as much a risk after maxing skills and weapons.
On the surface, Dying Light appears to be just a simple slasher game, but I find myself thinking out minute details a lot more than in this game. One small mistake out of impatience can cost you well over 1,000,000 Legend points.