(1) I have five circuits and want to run each one, one at a time, and then all five at the same time. My source is 12Vdc and 1500mA. The first circuit is 1.992 Mega ohms, the second is 3248 ohms, the third is 13.2k ohms, and the fourth is 0.247 Mega ohms and the fifth is .777k ohms. Now, the first four circuits use 5V and the fifth uses 9V.

First, how do calculate or get a resistor with this information to both limit the current for each circuit and make sure I get the right voltage for each circuit and then run each one at a time and then all at once.

(2) Next, if I have 12Vdc and 1500mA going into a resistor then to and led then to ground, how do I figure the resistor that will protect the lead?

(3) Finally, how do I measure I in a circuit?