[2020] Base plan

The staircases are a great idea. The important thing is that they have to form a clear path for the zombies. If one block of your stairs gets destroyed, it can mean all the zombies stop climbing the stairs and start trying to bring down the supports. So design the stairs in a way that zombies don't need to attack them, don't excessively damage the stairs yourself, either.

You don't want to go crazy with multiple layers of fences, because the number of blocks you need to cover to 'plug every hole' goes up with the square of the radius to your outer perimeter. Besides, as soon as they make the first breach, the rest of your fence loses most of its value. Or if you do go this route, use cheap traps like campfires and barbed wire, saving expensive traps like blade traps for the inner layer where you won't need so many of them.