I now finally got the first LoRa message send from my node through my gateway and visible at The Things Network.
My node device is the Adafruit Feather 32u4. It allows software switching between 915 and 868 MHz. The pinout of the Adafruit Feather M0 version is different and more common in the TTN forum discussions.
However, here is a summary of my config.
Arduino source is the tnn-abp (Activation-by-personalisation) created by Matthijs Kooijman (credits :-).
I have setup a single channel LoRaWAN gateway connected to the crowed source LoRa network The Things Network.
Hardware used is a Raspberry Pi and a Dragino version 1.4 (3.3V) Arduion HAT with a SX1276 chip. Got it via AliExpress. Credits to LogMaker360 for the video.
Update March 18, 2017
I had today to change the TTN server address to 126.96.36.199