30 horses? I am picturing 30 horses roaming free over acres and acres of pasture...or 30 horses in a not wonderful situation if they are not being cared for. It takes a chunk of change to feed a herd that size or a lot of good pasture. I would hope that the owner will give you lots of training in the grooming department prior to turning you loose. He will be responsible for your safety. You need to learn how to approach, halter and lead for starters. Then how to safely groom and work around a horse.
Good luck, stay safe, don't do stupid stuff (as soon as you learn what stupid stuff is) and always have your cell phone on you so you can call for reinforcements if the need arises.
If you ever find yourself in a fair fight, it's because your tactics suck. ~ Marine 1SGT J. Reifinger