As whafrog said, the Moria and Angmar sourrcebook wshould probably be step 1. He also pointed out that you need 1 hero for every 12 warriors in your army to lead them in a 'warband' (warbands affect initial deployment and nothing else). Since there are no goblin heroes amongst your 24 mines of moria goblins, i'd recommend picking up Durburz and a moria goblin shaman, they are the standard options for goblin leaders
This website:
http://lonelyknight.0fees.net/ features a link to a free army builder. This is helpful for finding out the points costs for your goblin town models, just incase you don't want to buy a £50 rulebook for the models you already have the profiles of
I wish you the best of luck, and welcome to the hobby