How do I determine the range of wire wound adjustable resistor?
Normally, I would say "read the datasheet" but there's not a lot there. 

The resistance will be adjustable down to approximately zero, you can figure on &lt; 10% of the full resistance for sure. 

Also when the resistance is set to less than the maximum you must limit the current to less than \$I_{MAX} = \sqrt\frac{{P}}{R}\$, so a 300W 100 ohm (full) resistor can only handle 1.73A regardless of the resistance setting. 

Here is a similar part, though the maximum current setting formula is a bit ambiguous. 

The setting resolution will be quite poor. Maybe you can count on 5% of full scale. Typically higher resistance resistors will have better resolution as a % of full scale, but not  in ohms.