Question: At this point, I have yet to actually touch an Arduino. I'm toying with the RPi3 along with Home Assistant, but I'm always thinking of ways to do useless things that are fun.

Let's say I had a kitchen with 32 cabinet doors and drawers and I wanted to make sure that each one had a switch that would detect a simple on/off state. That would translate to a map whereby a visual indicator would show that something's "ajar."

* Is this the best approach to achieve this goal?
* How many Arduino boards would this require, and/or are there other methods or concepts to achieve the same ultimate goal?

Thanks!

Answer: 
Touch less sensors (IR, magnetic hall), detecting drawer state.

1pc Arduino with I/O expanders to increase I/O ports.
Since you are just starting out, start simple and build from there. Build a system that can handle one cabinet door. By doing that, you will learn a lot of the basics, without the risk of having to troubleshoot a large complex system.

The most common sensor to detect open or closed door is called a [reed switch](https://www.sparkfun.com/products/10601). They are low cost and simple to use.

The number of Arduinos required is mainly dependent on how much wiring you want to do. I would probably choose one battery-powered Arduino with wireless communication for each door, to avoid having wires between cabinets at all.