WMG / Arrival

This is an alternative explanation for the creation of Starfleet.

Starfleet is originally created after Vulcans make first contact with humans, following a global nuclear war. However, once Starfleet comes into existence, an alien race that can see all time simultaneously and that has been/will be saved by Starfleet hatches a different plan to unite humanity and form Starfleet without the global nuclear war.

Aliens have taught humans to see into the future; humans will teach the aliens free will

Louise will realize that her visions of future do not represent an inevitable fate that she must carry out, but just one possibility that may be changed. She will invent a new set of symbols, consisting of multiple connected circles, to represent causality, future and past, possibilities, and choices. And maybe this is the gift that aliens will receive three thousand years from now - or that will take them three thousand years to comprehend.

In other words: the aliens are Wights, and Louise will become Culaina the Thunorg.

The Heptapods are Timelords

They even have similar circular written languages intended to represent a non-linear view of time.

The Heptapods are not as good as they appear

Just because they want to ally with humanity, doesn't mean that the threat that they will face in three thousand years isn't a enemy civilization or one that they enslaved. They might perceive all of time at once, and want to help humanity, but that help comes at a cost. Who knows if they have some less mutually beneficial arrangements with other civilizations who aren't the key to their salvation?

The Heptapods are four-dimensional beings.

They can percieve time non-directionally, and experience past, present and future simultaneously. However, they can only see one possible future: because they are four-dimensional. They only see events in one possible timeline. It's not that choices don't exist and the future is set in stone: other timelines are possible if different choices were made: the heptapods simply can't see those outcomes as it is beyond their perception in the fifth dimension. To illustrate, think of the dimensions in Flatland, where the two-dimensional square can freely enter and exit and percieve the one-dimensional Lineland, but in turn is himself unable to percieve the three-dimensional Spaceland. Perhaps the Heptapods have similar limitations in their perspective of time and the multiversal "hyper-time".

Abbot and Costello picked up English while on Earth.

Not that they were supposed to to maintain the challenge to spur Louise to learn their language but they correspondingly take in a lot of English during their communications and perhaps couldn't help trying to make sense of it. How exactly does that get Costello able to understand verbal English by the end? Well, the Heptapods probably also sent their best linguists.