Am I doing this right?

I don't drink coffee but I do drink hot chocolate.  So I followed the protein coffee instructions.

Made slurry with cold half-n-half and powder

Microwaved the rest of the half-n-half until hot and then mixed together very slowly.

Tastes fine.  But how hot is to hot when adding it to the protein slurry.

Betty

If it gets clumpy and refuses to blend, then its too hot....but making the slurry first helps prevent the clumps

130 F. 
I got this number off the Unjury chicken soup protein mix..  I add my powder to a cup full of
130 F water.  Just use a food thermometer.  I suppose your hot half & half could be a little hotter since you are adding it to a cold slurry.