Recently there was some unfortunate events that forced me to slaughter the whole settlement of Covenant and I wish to bring it back to life.

To start a settlement with no living people in it, is building the radio beacon recruitment thing the only way to get new npcs?

Also, is there a way to eventually expand your settlements building radius?

I Hope there's someone out there who explored the settlement building feature more then me and can give some tips on how to start a settlement from scratch.

As long as you can access the workbench, then yes.

As for the radius, I don't think you can change it.

From what I was looking at earlier today,expanding settlement radius and limits beyond what is currently in the game looks to be a only if you want to fry your cpu no I'm not kidding proposition, esp on borderline computer systems.

You basicaly have a fair bit of AI work going on with each npc in your settlement depending on there job, then you have the limits as to how big the active primary map can be. After all you have to load the terrain and every static prop item, and every movable prop item, and every loose prop item that can be put into inventory, and everything currently in a container.

That's not counting dealing with AI pathing, currently the settlements are set up in a way that more or less channels raids in more or less logical ways, with a minimum of Agro chaining caused by settlement raiders running around the perimeter pissing off every blood bug, feral, super mutant , and synth spawn within 100 m of your settlement.