can i use the 5v-output-pin for all of the components .....
did i choose the right resistor values?
can i use the same ground pin for all of the GNDs in the picture?
the digital pins do have a built-in resistor, don't they?
No, use 220R (that's 220 ohms)
No, if you didn't have the resistors you would short out the supply, you can't leave an input unconnected.
okay, so in the down right switch example, it doesn't matter if i put the resistor before the input pin or before the ground, right?but does it matter if i put it before or after the switch? i mean i'm still talking about pull down switching...
i'm talking about the right piezo, it's confusing me, i don't get the connections.
lets say, 20mA, wouldn't i draw 80mA from the arduino as i do this 4 times?
5v --------thumbtack thumbtack-------A5-----1k-resistor----GND
you will probably have to lick your fingers first. There is no danger to you doing this.