Reading a potentiometer on MCU
No, you don't need R1.  In fact, you can't have R1 if you want the output to go all the way to 3.3 V.

100 &Omega; is way too little.  That will draw 33 mA just sitting there doing nothing.  That could well be more than the processor.

The 8 mA figure applies to how much the pin can source or sink when configured as a output.  This has nothing to do with using it as a A/D input.



Use a 10 k&Omega; or so pot directly across 3.3 V to ground.  This is assuming that the A/D also uses the 3.3 V supply as its high end reference.