Initially I intended to use a FET but then learned that the FET appears as a capacitor for the AVR output and might damage it. Althoug I now have a satisfactory solution: is this concern justified?
No concern, the Arduino output pins have both active low and high output drivers and can easily drive most standard MOSFETS
That is what would have been a really good choice? FET, FET + Gate resistor, or NPN driver (as I choose)?
My favorite is N-channel LOGIC level mosfets. Be sure to obtain logic level mosfets instead of standard mosfets, as the standard one require +10vdc gate voltage to full turn on the device while logic level mosfets will fully turn on with just 4-5 vdc.
Lefty