Re: Do I need the 6th Martial Arts book?
There will be more martial arts styles in HSMA that what was in the 5E UMA (I talked to Steve about some of them). HSMA will also have 225-250 sample martial arts powers (written by me), arraigned in order from Real World, Cinematic, Wuxia, Video Game, Anime, and Ninja. Each section will present powers in the fashion common to Hero books these days -- Offensive, Defense, Movement, Sensory, Miscellaneous. There's everything in there from Acrobatics to the Thousand Sword Cloud.
So... yes.