Definitely karate!! Yeah bruce wayne learning from his master ras'al ghul who planned to destroy the Gotham city by his own clan "League of Shadows" Ok!
First we've to build up our body to 65kg, because Bruce Wayne has increased his weigh of body to 65kg in Batman begins. that means 65 Kg is bit ok from my personal view. Afterwards you should learn some good karate skills(fighting style) there are lot of fighting style which existed in this world.
Batman's first duty is terminating thugs and threats around the Gotham city and defensing the Gotham city from ultimate threats like super villains such as joker, kingping, penguin, harley quinn and more.
Right next step is bit complicated. We are not batman anymore because it's a fictional character so we need real batman costumes.. I've seen some people on facebook (users) had posted their different type cosplays. So we've to get a cosplay like batman indeed.
I have bought this from Amazon probably check it out here. This is very amazing batman outfit for very reasonable price. But this bit like old batman's costume by the way we need to be batman, it's doesn't matter new or old just batman lol :)