So, I'm running a spelljammer-campaign right now - so "Pirates in Space"? Basically.
The structure of my campaign is the following:
The Players started at level 1 and had no ship at all (woke up with no memories on an asteroid) - acquired a Space Hopper when they got to Level 2 (a small raft with which they can fly trough the asteroid belt, but not spelljam, so they were bound to very slow speeds and the local asteroid field).
From Level 2 to 4, they flew trough the asteroid fiel and had adventures there. Fighting off pirate attacks, visiting other settlements - helping out in their new Homebase in Planktown (a bunch of asteroid bound together by planks), looking for treasure, going fishing, getting killed by scavvers. The usual.
Then at Level 4 they got a mission that allowed them to salvage a spelljamming capable ship with a broken spelljammer helm (goes just half as fast as normal spelljammer helms and they can't go into the astral sea - so they can only explore the Wildspace-System they are currently in). Now, after using their new ship to destroy the pirate base in the asteroid field with the help of the Navy of Flumphaven, the asteroid field now slowly gets a little to small for their level (that's the point we are right now), now they will explore the whole system and find new places to explore and new pirates to fight and stuff. And when they have enough money, they can fix the spelljammer helm and go into the astral sea and visit other wildspace systems - like clown space (which they want to the destroy after the Circus was in Town ...).
So what, the campaign structure is, that I limit the players to certain areas by the ships they can use in that campaign. So at first they are limited to the asteroid they woke up on, than, when they have an asteroid hopper to the asteroid field, than with a broken ship the wild space system and after that the astral sea and other systems.
This helps the players getting used to the rules of spelljamming and the spelljamming/sci-fantasy quirks of the setting and also gives the players a sense of progress, it also helps me as a DM that at first I only had to really prepare the small area of space that they can traverse.
Like, getting your first small raft, and then you get a big ship and can spelljam (to your favourite Sci-Fi/SynthWave- Music?).
A non-spelljamming themed pirate adventure I would structure similarly.
Maybe they are shipwrecked on a seemingly uninhabited island, or they start in Prision on one of the non-pirate settlements and need to break out. They have to escape on a small raft/row boat or similiar and get to a pirate settlement, where they now can start their pirate careers. Maybe get a small ship that only can travel near the coast but not the high seas, have some adventures, get some loot and then they can maybe capture a bigger ship and now can travel the high seas.
For ship to ship combat - either do it cinematic or make sure that the ships can close quickly. With the 5E Spelljammer-RAW-Rules of Shipcombat, if one Ship would try to flee from the other, if would take like at leastt 40 to 50 rounds of Ship Combat to destroy the other ship, because they ship speeds are to samy and the damage the board weapons do, is too minuscle to damage the other ship. And there is also nothing in the rules to slow the other ship by shooting its sails. I homebrewed some stuff (magic sails to make you faster, Damage to a ship will slow it down at 75, 50 and 25% of total HP). And I let the PCs fire the ballistaes, so they can roll something during the chase.
But to be fair, I also set up the battles so that it is not a chase. The first space battle they PCs ended by waking up an asteroid spider while the pirate ship passed it and the Spider did their dirty deed. The second big space battle was a night scavver and it was a short brutal melee fight (that the Wizard started and died by ...), the third space battle was 10 ships (1 player ship, a friendly adventure group ship, 8 ships of the Navy of Flumphaven vs 1 Pirate ship) which was short and brutal - and that was basically it - all other fights were on the asteroids.