the power depends from the values stored in the image, so difficult to say, but since you can change the power slider interactively, it should not be a great deal to find the correct value.
Aboute temperature, please, use the Texture Emission node, in this way the temperature is bypassed.
The Kelvin temperature is related to Blackbody emission node, and used to mimic the different light sources.
About shadow catcher, you need to enable the Shadow catcher/Matte option active in the Common tab of a Diffuse material, or use the Render Layer technique:
https://docs.otoy.com/Cinema4DH/C4DPlug ... Passes.htm