I've seen the AIR2's used as a 'third' option. So the diver will have his octo and primary, and an AIR2 as an inflator.
I would not suggest using the air 2 as a secondary without backup.
Ofcourse you can do whatever you want, but they don't really breathe that great for long, and you'll constantly be deciding between breathing comfort or an inflator that scares the holy bejeebus out of you because it will freeflow so easily when entering the water.
For the primary length I would suggest going for 3 foot minimum (so 90cm) preferrably even 1m or 1m20.
When diving ffm I dive my octo with a 1m10 hose with an omnidirectional second stage routed from the left.
To tuck in the excess hose I suggest to just tuck the excess in your waistbelt. it easily flops out when needed and stays nicely tucked away when not.