Living in Calgary myself, I can give the following advice.
It only really starts getting very cold at the end of Nov. Up until then, the weather is ok, with a cold day here and there.
The cold is described as a dry cold, with little moisture.
If you are going to be here for 6 months, you will definately need some good clothes and shoes as you will be here for the coldest months.... Jan/Feb/Mar. The cold is not endless, more often than not the spell is broken up by a warm wind called the Chinook. It can raise the temperature up 30 degrees in a couple of hours. Its awesome. -20 C one moment, turns into a pleasant +10 c later.
clothes.......I am from Africa, and I find that a good jacket, with a good shell to break the wind is important. I have a goose down jacket. nice and warm. thermal underwear <--Helly Hansen. Maybe some ankle high boots, to prevent snow from falling in.......mind you Calgary does not get much snow. Get gloves and a toque.
The warm clothes is only necessary when walking outside, once inside, all is good, as buildings are well heated/insulated.
do not go overboard buying stuff. If you need stuff, then wait till you are here to buy them.