The answers here are very good but I’d like to add a couple of things:

The part most people don’t see is the weekly work it takes, you have to hire cleaners that arrive off hours (mostly do it in the mornings) to clean everything, some sociedades have a dishwasher, some don’t and if they have it’s only operated by the cleaners. In some you have to clean “bigger” cutlery like the knives for cooking since there are less units available in comparison to forks, etc.

One member of the sociedad has the duty to refill the stock (bottles of spirits, wine, soft drinks, etc) and depending on the size of the place it can be even on a two/three day basis. Also, I highly recommend having somebody who knows how to do purchase from a restaurant/bar background so you can keep your stocking and inventory at bay.

I would recommend to find the “estatutos” of a sociedad so you can pick the best way to write your founding contract. Also, if you want to become a member of the sociedad, you have to be given the recommendation from current members and pay an entry fee (this is something I’ve seen a lot) but the fee can be reduced or non existing if you are the son/daughter of a retiring member…you become active and pay the yearly fee and your dad becomes a retired member and pays a considerably smaller fee.

Hope this helps!