but we're ready to work and learn.....
Let's start with this, then. One period is enough. Three indicate that the rest of the sentence was omitted because it went without saying. Five periods don't mean anything.
One does not build a big project. One assembles a big project from small projects. Powering and reading a PIR sensor is a small project. Wiring and reading a magnetic switch is a small project. Wiring and reading pressure mats is a small project. Ditto for gas sensors, smoke detectors, etc.
Flashing and LED when a condition warrants is a small project. Triggering a water sprinkler system is a small project.
Get each of these small projects demonstrated, and then it becomes easier to assemble the big project. Jumping into a big project without knowing how to do the little projects is where you are setting yourselves up for failure.
When you get all the little projects working individually, you'll see that there are issues with connecting them together. There are a finite number of pins. If you have more inputs or outputs (or both) than you have pins, you need to see whether multiplexing is an option, or is a bigger or another Arduino needed. If you need another Arduino, then you have another small project - getting them to communicate.
Once you have the system working standalone, then you can internet it. That's another project. Whether it is small or large depends on the skills you have developed by that point.