One of the great functions of being in a guild is that you can get skill that are effective in each and every battle that you enter. All skill max out at level 9, each level will have to be upgraded with resources and ore as well as learned. Learning these guild skill will cost you guild coin but they are permanent.
In your Production Base is where you learn your life skills for Cooking and Forging. These skills do not go past level 5 so there is no need to upgrade the building above Level 5. Level 5 you can learn Orange Recipes which have not shown in any guild shop to my knowledge.
Guild Battle Skills
In the Military Base is where you learn Battle Skills, these are all maxed out at level 9. They will cost you guild coins to learn each and every level.