How many hours per week would a person in a 100-person commune need to work for the society to function, assuming the work consisted of the bare minimum of self-sufficiency + tax (minimum farming, carpentry, plumbing, tailoring, etc.)?

I have no idea what it takes to be part of a commune, but I have some idea of what it takes to provide food for 100 people. It takes a system that starts with highly nutritional annuals and gradually is replaced by perennials. One acre of wheat provides around 1,000 lbs to one ton of food, one acre of Chestnuts provides 4,000 lbs of food, and only gets better with age. The world record Chestnut yield is 1,000 lbs from a single tree. If you can replace your staple annual crops like corn and wheat with perennial Hazelnuts and Chestnuts, you will decrease your workload on the long term by an incredible amount, and should be able to feed many more people. Plus, no one can really grow other crops under wheat, or graze animals through corn, but you can grow your medicinals, other crops, and graze animals under your trees and bushes without too much work at all. It takes quite a lot of work to establish, but once established should take each member just a few hours per week. If you have more intense needs, like you only have 25 acres for these 100 people, it will take more work to keep up on farming. It is possible to produce enough food for a family of four on one acre, but quite a lot of work. It is much less work to produce on one acre per person, and will be more of a gathering/canning type lifestyle where 20 hours per week is food harvest divided between a family of four, and anywhere from 3-10 hours of canning, fermenting, and dehydrating work after food-bearing trees, vines, shrubs, groundcover, mushrooms, and animal systems are established. One could hardly call a stroll through a food forest, eating berries and picking leafy greens, work. The initial work shouldn't be too bad with 100 people at your disposal, but expect to utilize as little annual space as you can manage to feed 100 people so that perennial systems can establish in the rest of your space. Alternatively, you could plant a row of trees every year under swales and annual farm around the trees until they shade out your annual crops and begin bearing. As for making clothes, building houses, etc. I have no idea, except that building houses takes 20% framing, 10% roofing, and the rest is finishing the inside in a "modern construction" home. It costs thousands of man-hours. In cob building - 10% framing, 10% roofing, and 80% playing with mud inside and out. It costs far fewer man hours and much less sophisticated knowledge/tools.

Look up what is known as a Kibbutz, that should give you and idea of the necessary amount of people for the survival labor. Then figure in about 15% more than that to cover the taxes

Thanks for inviting me to answer. Mateskon practically answered to the fullest. Actually it is not possible to tell about clothes, building houses, etc. Unlike food, they have too much variation today. gave the excellent example of your idea in deployed state - http://en.wikipedia.org/wiki/Kibbutz. For practical purpose examples of such community based models usually runs today around Spiritual communities - ISKON is a good example. But they actually use a modified version adding import, insourcing etc. practical methodologies are used.