1. 14 pieces times lets just say the augment which im guessing you would use the Willpower one, and for each piece that's an extra 18 willpower and 12 endurance which equals...252 more Willpower, and 168 more endurance(1,680 more hp, EVERY point counts!) + all the extra stats and bonuses you get to have and keep in your WH augmented gear, say I would say yes...
2. You can buy/use WH gear (No requirement on valor rank).
3. Refer to #1.
4. And just to clear things up for you the Set BONUSES do not carry over from Battlemaster mods.
5. Do your research next time.