Ok, never buy transformers on ebay. I am an advocate in many ways for ebay, but not when it comes to this. If anything goes wrong with that transformer in a year, what are you going to do? You'll have to buy another and it will come out of your pocket. Remember, the transformer is the heart of the system. Would you buy your pacemaker on ebay??? Buy as you need them, price doesn't change often enough to waste space on stocking them. It would not hurt to have one of each on hand for emergancy though.
As for wire, I always buy in 500' rolls. You have less waste that way. I go through about 20,000' per year so if you can buy that in bulk, you can save some money. Copper prices do change often and they are not going down.