iPhone development on the new MacBook I want to do iPhone development with the MacBook. The MacBook only has one USB-C port, so I may need a USB-C adaptor to load my apps on my iPhone.

Is the USB-C adaptor necessary to load freshly compiled iOS apps on my iPhone?
You really need to make up your mind whether you want the latest and shiniest product, or whether you want a good development machine. Once you use Interface Builder, a 15" MBP is the smallest that is usable without an external monitor. And once you use an external monitor, you are connected to a desk, and the portability doesn't help much. 

The new MacBook is targeted at certain use cases. Serious software development isn't one of them.