This whole thread is a royal mess. Chain tensioner, manual front shifting, swapping cogs... Why not just stop screwing around and put a derailer drivetrain on? They use these handy little things called shifters that can be mounted on the downtube or the bars. And they give you all the range you'll ever need if you use a triple up front. The system will also be lighter than an IGH.
What am I missing here?