Absolutely a mini and an extension cap. If, in the future, you find yourself draining an 18490 faster than you'd like, you can put a Tatroe extension ring between the Mini and the extension cap to use an 18650. This way, you can run it in whatever configuration, depending on your needs/wants/desires at the moment.
Regarding the crop circles, couldn't care one way or the other. At the end of the day, it's the electronics I was after. the rest is just a tube to carry a battery and a connector for my atomizer.