A question:
My kit came with a 1kg bag of glucose powder, but my instructions don't mention using this until siphoning into the keg.
However, surely I'm supposed to add glucose when making the fermentation mix? I created the fermentation mix last night, should I add some glucose powder now, if so how much?
You need about 3kg-4kg of malt extract to make a 5-gallon barrel of beer. Adding sugar is unnecessary, but you may choose to do so to make a stronger, drier beer.
Sugar can also be added at the barelling stage. This is called priming sugar, and is designed to give the yeast a little more food to produce some CO2 to give the beer a bit of condition (fizz). Strictly, it's not necessary - a good beer made from top-quality malt should need no priming, but it can be useful if your beer is a little flat.
A kg of priming sugar won't create beer. You'll have a beer-pop. I hope you have safety release valves on your barrel!