How much of that can you code already? What you sketch out is not nearly a beginner project.PIR only signals when it detects change. What keeps the lights on when the subject stands still?PIR is low power but you need a datasheet for yours or testing it to say how much power it needs.Suppose PIR only runs 10 times a second?Relays should not be switched too frequently. A minimum OFF time in software can handle that.Using bits in variables to hold binary sensor readings, 1 bit per sensor, bitwise logic can be performed on all of the bits at once. It beats writing if statements with line after line of conditions and matching parenthesis to do the same with a logic operation. Are you up on bits?Have you done anything with wifi?
I didn't build my home automation system... I have:X-10 Motion SensorRF to X-10 Receiver/TransmitterX-10 Compatible Dimmer/SwitchIn my setup the motion sensor only controls one light. But the RF transmitter receiver also works with other wireless controllers and other dimmers, and the dimmer can be operated by other controllers/timers, or it can be operated locally.