Your substitution of the sugars and enhancer with DME is fine. I found the Canadian Blonde kit a bit anaemic so adding malt instead of mostly sugar should address that to some degree.I've done a bit of reading around the Cooper's Canadian Blonde kit and how others have modified it slightly. I'm thinking of buying the kit but replacing the 1kg of brewing sugar and 500g of brew enhancer it recommends with 1kg of Extra Light DME. I also plan to replace the 7g of yeast with 11g of Nottingham yeast. Finally I plan to add 1 Coopers Carb drop per 500ml bottle for some fizz.
Provided that sounds all ok, it's just the temperature and length of time I'm stuck on. Recommendation here was 23 degrees, the kit recommends 21-27 but others have suggested 17-18 if you modify the instructions as I have above. All have varying brewing times too.
Regardless, my garage is currently 9 degrees (it's a bit drafty in there), my house about 20. So neither seem ideal. I feel I may need to mod a small fridge to provide me some kind of temperature control. It will be useful for when I do get a bit more experienced and try some lagering. Or, do you think I can get away without that to begin with when using the Canadian Blonde kit?
Next there is no need to use carbonation drops, Ordinary table sugar is fine. Its much cheaper and you can more easily adjust the amount of priming sugar to suit your style of beer. If you are using 500ml bottles half to three quarters tsp sugar will be sufficient (more sugar in that range will give more carbonation).
And although its up to you, in my view there is no real need to change the kit yeast, only if you intend to ferment at less than say 18*C. Coopers kit yeasts are OK and usually give good results, certainly in my experience.
As far as temperature is concerned, in simple terms the lower the fermentation temperature the longer it usually takes, but the difference is usually measured in a few days, less so weeks. And fermenting at lower temperatures is said to produce a cleaner taste which suits lagers rather than fruity bitters.
My advice to you is to get the basic equipment you need to brew your first batch, get the necessary ingredients and get your beer going. With or without temperature control, provided the background is warm enough you will still brew beer. And having done that and learned a lot you can then turn your attention to the more detailed aspects of homebrewing, of which there are lots, just like opinions on this forum