Sander, What rear pully to use depends on what overall ratio you are looking for. In the UK with an Axis 2 it was not unusual for us to run 31 tooth pinion. We would now use the 20tooth rear pully and then use 3 teeth smaller (28) to attain the same ratio. This obviousely has benefits for rotating mass ect. Also with a bigger pully the transmission should be more efficient as there isn't such a harsh bend in the belt. If you generally use a much smaller pinion then would be worth consddering the smaller pully.
Belts, I wouldn't recomend running the grey rear even with 12 turn. The grey front is fine though and it can still be run as loose as you want.
The steering link can be adjusted, it is essintially 2 ball cups with a theraded bar in the middle. If you want to lengthen it then you can un-screw it a little.