1. Yes. However, knowing which possible starters you are using might be helpful to know.
2. For both boosters and starters, any available can be used. However, since A/B and C/D are no longer in print, that doesn't leave many options.
3. Since the G/H starter decks come with Warrior-Class characters, I don't see why normal rules would not apply. Perhaps you were thinking of Booster Draft?
4. There could always be a situation where battles are won by the numbers, more so in sealed & booster.
5. You can only trade with your first opponent (at the time you create your deck).