Your Logic doesn't make sense, when he uses the bombs he stayed on the planet while it exploded, I doubt if he didn't like the feeling he stay on it . It's much more convenient for him to destroy the planet with his hammer rather than than having to place bombs on them which could have delayed him and allowed Galactus reach him before he had finished.
Also your hammer and nail logic doesn't agree with me. It would only apply if the nail had no real power of it own, but we know that with the Power Cosmic Stardust has great energy output. So, Bill channeling his own energy with the Power Cosmic therefore increases the sum total energy output which led to the planet's destruction and if he could destroy the planet by himself why didn't he just do so. It's not really hard for him to strike the planet with Stormbreaker alone.
1.Then give Yourself any other reason. I wasn't serious, because it wasn't a real question. BRB wanted to destroy planet - he did it, so there is nothing to talk about.
2.Until You can prove that he used its power and that he even can use its power - he didn't use it. There is nothing even suggesting he did. Besides You forgot that his point was to win a battle, not destroy planet or not.
He can combine his energy with the energy held in Stardust staff. Also what is the point int his case of using it as a "nail" so to speak?
1.It is more epic.
2.How he can combine his energy with her? And why he should do it? His last strike was more powerfull than one that destroyed planet. When he destroyed planet, he wasn't even boosting it with energy, while his last blow was charged.
He can beat any of them one on one, but as a team the Annihilators win pretty badly.
I don't see how it is even possible for him to defeat people who can depower him (Surfer and Quasar).