Terraria is… basically nothing like a factory game? You can do some crazy stuff with the logic gates but that is mostly a hold over from Terraria being so inspired by Minecraft. But Terraria also had an actual progression system while Minecraft was still almost entirely a sandbox game.

With Terraria? Go look up what defines a “room” (I think the next big patch will have the NPCs help you with that in game) and always have a spare “room” in any housing area. That is where new NPCs will move into.

And then just play the game. Explore caves. Look for loot. Get your poopy pushed in by a boss. Progress will unlock new NPCs who will, in turn, point you towards other activities that will reveal new bosses or encourage you to seek out and build outposts in new biomes and so forth.