Current drawn by microcontroller
This isn't specified directly in your datasheet, but there are a couple of clues in there.

First, there's a spec for the maximum resistance of the sensor or signal conditioning circuit that drives the ADC:



where Note 8 refers us to Figure 11:



The limit on the source resistance tells us that the maximum input leakage current, when run through a 40 kΩ resistor, won't cause a voltage drop big enough to disturb the ADC reading (by more than the specified absolute error of counts). Taking the minimum VDDA value of 2.6 V, divided by the resolution of the ADC of 1024 levels, this implies 

$$I_l &lt; 4 \frac{2.5\ {\rm mV}}{40\ {\rm k\Omega}}$$

or about 252 nA.

From this we can infer an input resistance of 10 MΩ or greater.

But note in the input equivalent circuit, you must also consider the input capacitance if your signal is varying somewhat quickly over time.