In my sci-fi universe there were two classes of warships of importance for the hero empire- Stratodragons and Klee-Fangs.
None are the size of Picard's Enterprise or an Imperial Star Destroyer.
Stratodragons were the larger ones, swift, armored, shielded, and heavily armed as well as having "starburst" ability to take out any nearby fighters. Each could carry 12 fighters and three bombers. They were just big enough to carry solarian bombs and time missiles. They vaguely resembled dragonish pterodactyls.
Klee-Fangs were a smaller class, especially fast and always appeared in packs. They would swarm around enemies, taking bites out of the enemy (figuratively speaking), attacking from all directions at once. They were also meant to terrorize enemies because of their ruthlessness. Each could carry three fighters.
All of these ships were also equiped with missiles and chain guns.
Since that empire was not overly large and they had no interest in expanding their territory the fleet could easily protect the entire empire. Each planet also had its own defenses, including a navy and an air force.
Their main enemy was a race resembling Ancient Greece but high-tech, not unlike "Ulysses 31." The main warcraft they had were not ships but warbases built on asteroids, resembling flattened globes. They carried many Trident, Sword, and Archer class fighters, as well as Minotaur and Satyr walking war machines for invasions. They also carried swarms of mechanical "Harpies," small and very maneuverable. These resembled long-necked bats of bronze and were armed with sonic disruptors and energy cannons (carried). The largest warbase was the Acropolis Command warbase, easily as massive as an Imperial Super Star Destroyer. These warbases were armed with a sort of lightning cannon.
The dimension all of this took place in was a weird void with an endless flat land and atmosphere so normal astrophysics did not apply. It was not possible to fly more than ten miles above any land area.