The binding is installed. Rich was just telling you that (because it is a 1.x binding) you will not see any Things in the inbox. Just start configuring your items in config files as you know it from openHAB 1.8 / as described in the wiki article.
There is no openhabian user and non is documented in the openHABian instructions.
Samba is enabled by default.
This is not needed.
http://docs.openhab.org/addons/iconsets/classic/readme.html
The binding config (if you want to create it) has to be called /services/gpio.cfg and inside you need to in return remove “gpio:” from all config lines.
No. What makes you think that?