Despite being a fundamentally simple device, the modern high performance brushless motor is actually a subtle and somewhat complex device, where compromise is the aim of the game!
Factors such as lamination thickness, insulation, mechanical retention and material all make large differences to the performance of the eMachine. As do many other factors such as the winding scheme and the magnet geometry.
My suggestion other than doing a lot of Googling (plenty of people have built their own brushless motors on a DIY basis) would be to buy a small off-the-shelf motor from one of the usual suppliers, and take it apart and perhaps modify it to help you learn what factors matter the most. It's a big topic, and potentially a lifes work, and these days, things like 3d magnetic simulation increasingly are used to optimise the performance of the eMachine. And of course, once you have the eMachine itself, you need to drive it, so rapidly you'll find inverters and brushless motor drivers become an interesting topic!
one source for really cheap brushless "motors" is to use motorbike generators, cheaply available on ebay:
![](http://i.ebayimg.com/images/g/FjgAAOSwRE9bqdR6/s-l300.jpg)
You'll need to sort out a basic bearing arrangement because the rotor is normally carried directly on the crankshaft, but that's not too difficult, and then you have a cheap motor to play with
(they are not very efficient, but great for messing around with!)