What is the most time efficient way to serve food fairly to ~100 people?

Seems like a good use for "family style". Bring platters or bowls of each dish to each table. Then at that table expect decent behaviour such as passing the platters around so everyone gets some. It shouldn't take long to fill and distribute bowls or plates of things. Carving meat into slices might take a while but would have to be done even if people were lining up to get their individual portions.

If some people weren't good sharers you could use assigned seating and put the non sharers at a table that gets its platters last.

As Kate said, "family style" seems ideally suited to this situation. The problem with "family style", though, is that you need a lot of serving dishes. If you have 8-person tables (which tends to be the standard), for ~100 people you need at least 12 tables. Multiply by 4 dishes per meal, and you're at almost 50 serving dishes (and the same number of serving spoons), which all need to be acquired, filled, distributed, and then washed.

If you don't have the resources to accomplish that, the other option is to scale it back a bit: have multiple serving stations, just not quite that many serving stations. Even just utilizing both sides of the serving table (either with identical but separate dishes and spoons on each side, or just orienting the larger hotel pans crosswise and putting spoons at either end) should cut your serving time almost in half. Oddly enough, the biggest problem with this is training people to actually use both sides of the table, especially if they've been used to the one-sided method.

If you add another serving table, again using both sides, you will have theoretically cut your serving time down to 7 or 8 minutes - not quite a 5-minute free-for-all, but way more equitable. "Two tables, both sides" can be achieved with 8 hotel pans and 16 serving spoons, which ought to be well within your resources. The drawback is that you now need to have two queues, and you can end up with one table running out before the other one does, and other such "messiness".

One trick that can be used no matter how many serving stations you have is to not put all the food out right at the beginning. Instead, periodically replenish the serving dishes as they start running low. People are less likely to take more than their share if doing so makes a noticeable dent in the amount left in the pan. This way, even people at the end of the line will have a chance at the desirable items, and there may even be food left for second helpings.

two ideas come to mind.

1. I dont know how many dishes get prepared, but if it's a limited selection, perhaps you can have someone prepare plates and people just have to come up and pick up a plate rather than standing there and picking up individual items.

2. can you create a 2nd serving area? If you can have two tables where people help themselves instead of one, should cut the time in half.

Since it is a cooperative, could you devise a plan for a rotating cooking/plating/waitstaff?

Unless the "more popular" items are all more expensive to make, why not make sure that roughly the right amount of each dish is prepared in the first place, taking popularity into account? If "food runs out", take note and prepare more next time, if there are significant leftovers, prepare less of that item next time... "Fair share" sounds elusive with perishable food since what people want is the amount of each preparation they want to eat that day. A "fair share" distribution would be more applicable if you gave them universally useful materials or money...

The more I think about it... wait staff is your answer.

Example: West Point Military Academy feeds 4,000 in one sitting. They do it with wait staff.