1) "The battle took place *in* the Pacific Ocean." You're treating the ocean like a location, so it is no different than saying "The battle took place in England."
However, you say either "We are going to fish *in/on* the river". There isn't a huge difference but to me "fishing in" emphasizes the actual body of water while "fishing on" emphasizes the actual act of fishing.
2) You would have to say "Don't pull *a* mom and tell me what to do." But "pull a" can be used to mean "act like" or "imitate".
2.5) "T-mobile does *provide* phone and internet service". Because you already conjugated "does", you don't need to conjugate "provide" as well.