Yep, as mentioned, it's the Emergency hydraulic hand pump, used in conjunction with the selector switch for flaps and gear (86).
Here's the missing part of the key (it was on the next page, which I hadn't noticed!), and the first part, just in case.
I had a quick read of Eric Brown's account of flying the Arado, and he mentions the official pilot's notes that he eventually found. Looks like we were right about abandoning the aircraft in flight - seems there probably wasn't much hope, as the notes instruct that, the control column has to be unlatched and thrown forward, the roof panel jettisoned, and then 'try to dive sideways, under the leading edge...'!!!
No mention of type of parachute, although the drawing with the vac-form canopy instructions shows a 'bucket' type of seat pan, and padded back rest, and the cutaway I have, from rear 3/4 starboard, only has the seat 'bucket' in view.