for the chain, considering its length, I would consider running the rising side on one tube and the falling side in another. In one tube I'd be concerned that over the length the whip of each chain half would become entagles and cause some damage. For the lubrication system, you could consider using a cotton or wool cord (wick) with one end submerged into a bottle of old engine oil and the other end dangled out of the top and in line with the chain/sprocket (best make something to hold the wick in place). This will create a drip feed. as the smal amount of surpluss drips off the chain you can just mop it up with sawdust/sand/old rags. you could even leave enough material to soak up enough oil that you only need attent to it once in a while. For stopping the drive, some form of clutch would be in order. perhaps you could use the derailleur set up off a bike. have one sproket fixed to your motor shaft, and the other connected to a free wheeling shatf. when you change gear, the drum disconects and simply free wheels the spare sprocket.