[tka]

>> 1) The effects of the endless bag of wine don't stack (seems like it should)

AFAIK the effects should not stack if you put 2 bags of wine on one commander.

>> 2) I have 5 commanders each with a endless bag of wine. Yet, the 'supplies' in the province they are in is reported as only 68, and my army is starving with a usage of only 127.

If you take of those endless bags of wine you will notice that supply usage is 127+125=252. Endless bags of wine, Cauldrons of broth and nature mages decrease supply usage. They don't increase province produced supplies. The same effect after all.