Defense is limited to a few items. You can use them creatively to gain a great advantage or use them poorly and have stuff broken all the time.

Technically you don't even need walls if you can just prevent spawns and keep your stuff and yourself hidden.

This is not a PVP game so you don't need to worry too much.

There are no friendly NPCs to hire or use. You do the work. One great plus to this is that you don't need additional resources to repair and everything beyond consumable fuel is returned when deconstructed so you don't need a ton of additional resources to just keep going. Brilliant game design in my opinion. Keeps things simple.

Your goal is progress through the world through the different environments or "biomes". Each one has its own boss to beat.. the resources your gather open up your building/crafting menu and expand as you reach new and more difficult areas.

Many people get stuck on the idea of having one main base but really you don't want to settle on a place too early... start out thinking you are just living out of a small cabin as a temporary home until you progress. Expand as needed and where it benefits you in moving stuff around.

That is how I see the game.