Bohemia posted these wiki articles about the above:
Weapon configs: http://community.bistudio.com/wiki/Arma_3_Weapon_Config_Guidelines
Character modelling: http://community.bistudio.com/wiki/Arma_3_Modding_Characters
Weapon configs: http://community.bistudio.com/wiki/Arma_3_Weapon_Config_Guidelines
Character modelling: http://community.bistudio.com/wiki/Arma_3_Modding_Characters