Yes, once it's cooled down to about 20 degrees C, add some more yeast - it's unlikely the original will have survived at 75 degrees C.
And, yes, once it's fermented, add sugar to the barrel before syphoning in your brew. If you boil the sugar for a few mins in a little water first, then pour it into the barrel, that'll help it mix with the beer. Fermentation will kick off again and within two or three days you should notice your barrel swelling slightly with the pressure.