Oil on the surface of the bean is primarily a function of degree of roast. That's why city roast is not oily and french roast is. Here's a good link - check rasquals response.
My first dinner post after lurking for years. Locally grown pork, grilled eggplant and crimini mushrooms, potato pave and great local tomatoes. The pave recipe is from Thomas Keller that I have re-purposed for about four meals.
If you are new to the process don't be worried about over roasting. I think you need to burn a batch or two to get a feel for the process especially if you are not monitoring temperature. With the method that you are using you will enter each roast stage somewhat gradually with each stage not as clearly defined as you would think. The roasts will always be (at least mine) less uniform due to limitations in the methods we are using. Here is a good link from SM to help you evaluate your efforts. http://www.sweetmarias.com/library/category/content-tags/degree-roast and roasting tips for air poppers http://www.sweetmarias.com/airpop/airpopmethod.php
I've been home roasting for about six years using Sweet Maria's offerings. I will order the 5# bag of Moka Kadir or Espresso Monkey blend and the 8 lb sampler and the combination qualifies for flat rate shipping. The beans are of the highest quality - well sorted, no trash or partial beans. The espresso blends are usually roasted just a few seconds into second crack and the single origins are generally roasted as recommended. Last nights roast was a Sumatra Lintong Tano Batak from the last sampler roasted to FC++. I use a stove top roaster (Back To Basics) and roast 1 to 1.5 lbs at a time using a gas stove and 650 cfm hood vented to the outside. I have found that I get a more even roast with these weights as opposed to less than one pound roast. I roast in the evening and the time to roast a single origin is usually one beer and espresso 1.5 to 2 beers. That gas cooktops puts off a lot of heat! I step outside to cool the beans down by transferring them from colander to colander in front of a floor fan. It is amazing how much chaff is produced. My espresso setup is a Mazzer Mini grinder and Quick Mill Vetrano machine from Chris's Coffee Service. The equipment's been bullet since it's purchase in 2007 and the combination of good equipment and beans has produced a lot of great coffee.