The voltage "tax" makes sense and I like the idea of being able to use only one LED for some of the smaller building so i will stick to the 5VDC LEDs as you suggested. What is the advantage / disadvantage of selecting a higher voltage 16 or 18V instead of the 12V? Higher voltage means more current available. I would be able to add more accessories to the power supply? I know there is a limit based on the wire size I have. Many years ago I had been thru multiple different classes that covered ohms law and I struggled every time. Hated doing the calculations. I would just remember the rules to pass the test. And the theory seemed to change based on who was giving the class. I could never figure out if electricity flows from + to - or - to +? If AC changes polarity with each cycle how does it flow at all? OK just kidding. All I care about is if the circuit is complete it flows.
So know I know what I need for the LEDs, voltage regulators and a power supply. The discussion of the system architecture would not be incomplete without talking about circuit protection. What is necessary and where in the circuit makes the most sense. Does a lap top power supply have any kind of thermal/over current protection? My main concern will be protecting the wire from overheating as it does travel inside of an insulated wall from shelf to under the bar.
Are we ready to talk time delays yet? Power is fun but controls are cool. 
