Toph required direct contact to bend metal at first, but she got better with it over the series. It's a new ability that will obviously be developed over time.>>98566688
Generated lightning =/= real lightning. Otherwise Zuko would be like mach 180+ for running in front of Azula's bolt in the finale. I doubt they'd be able to react to bullets, perhaps a very talented metalbender could affect the trajectory slightly at most.