For exact thrust power, I figured it out.
It's all basically more or less the same, by the way. Save for Firebrand, which is slowest of us by far.
Crescent Corvette has exactly 1 thrust power. 140 tiles, 14 engine tiles.
Firebrand Destroyer has about 0.725 thrust power. 193 tiles, but still only 14 engine tiles.
Spearhead Heavy Cruiser has almost a full thrust power; 0.969, with 289 tiles and 28 engine tiles. Yes, the addition of a single engine tile would put it to 1 exactly.
Hunter Killer Destroyer is the fastest of the lot, barely, with 1.024 thrust power. 205 tiles, 21 of which are engines.
Speaking of which, the HKD and Spearhead Heavy Cruiser should be the widest of the lower, the Firebrand being the sleekest; HKD and SHC are both 21 tiles wide at their widest points, while Crescent Corvette is 19, and Firebrand is 13. The Spearhead would of course still be the longest, however, being 22 tiles long, while the Firebrand is similarly long at 18. The Hunter Killer is 13 tiles long, much stubbier, comparable to the 12 tiles long that the Crescent Corvette is. Fittingly, I suppose, considering it's a modified version of it.
In short;
Crescent Corvette: 19 tiles wide at widest point, 12 tiles long overall.
Hunter-Killer Destroyer: 21 tiles wide at widest point, 13 tiles long overall.
Firebrand Destroyer: 13 tiles wide at widest point, 18 tiles long overall.(yes, it could fit anywhere the crescent corvette could, basically, just turned sideways)
Spearhead Heavy Cruiser: 21 tiles wide at wide point, 22 tiles long overall.
And now for my analysis of the ships.
The Crescent Corvette is what you'd expect it is; a general-purpose, cheap ship not specialized in any particular direction, decently fast only because of it's comparatively small size. It has a great deal of room for customization, boasting many empty hallways whilst still accomplishing it's purpose admirably, that of being a starter ship for beginning captains; it makes up for it's lack of overwhelming armament with the ability to, in all likelihood, go fairly unnoticed in battle, as well as achieving ambushes with ease due to the Blackout missiles. Whether it can follower through is another matter entirely...though given enough of them, it is more than likely, even as fragile as they are, lacking hatches over their weapon ports.
The Hunter-Killer Destroyer is an adjustment on the Crescent Corvette, apparently a standardized set of such, keeping the same speed and flexibility inherent in it's base design, whilst granting it an improved armament and boasting heavier armor, an entire plating of such over the front, to keep it alive for the time needed to rip apart it's prey. Suited for running down isolated ships or pursuing stragglers in typical use, it also has use as a harassment vessel in heavy battle; though it's armor can keep it alive against single targets for the time necessary, larger battles take much longer, and it's shields cannot withstand focused fire upon it. As such, it should stay out of the main line of fire, maneuvering to flanking positions and firing opportunity salvos at enemies with exposed sides or engines to further increase their speed advantage, using it's lasers to take potshots at the enemy in the meantime. When ships have been weakened, or are exposed, they can also dive in for the kill, loosing their weapons time after time with lessened risk of danger from using up their overdrive(and thus, their shields), as their weapons take up significantly less energy than their pulse cannon counterparts. Their railguns have an advantage here, in being able to blast through shields to pound at armor without caring for the shape of the shields, though the strength of such weapons is of course increased when the shields have been breached. However, the limited ammunition available to them further cements their role as a ship meant to fight solo targets in short battles; the continuous fire needed to fight multiple targets is not something available to them, and unless supply vessels are close by to reload them, they will suffer.
The Firebrand Destroyer, on the other hand, is quite well suited to such large engagements, even with a similar shortage of ammo. Speed not typically being necessary in such pitched battles, it instead uses the space(more likely money, since engines give so much thrust per tile) on stronger shields, an EMP cannon, and an exuberance of missile launchers. With such defenses, combined with the thick plating interspersed with the space needed for it's missile launchers, it can afford to be cautious, as it is meant to be used, waiting for the ships of enemy shields to be depleted before striking. In the meantime, it can use it's EMP cannon and lasers to assist with the destruction of such shields, loosing a vicious missile volley against any foe fool enough to allow(or misfortunate enough to have been unable to prevent) their shields to drop completely. Rather than focusing in on one target, however, the Firebrand is suited to switching targets once it's deadly payload has been delivered, relying on the flames and destruction induced by their massive volley to finish off the unfortunate victim. To further assist whilst reloading their primary weapons, and to ensure their weapons do in fact hit and cripple, their EMP cannon is also used with this fatal strike, preventing the shields or any makeshift point defense to be used as the missiles close the distance. And then the wait begins again, for an opportunity to cripple another ship, perhaps so vessels such as the Hunter Killer can give the finishing blow, ripping the enemy apart to leave it a floating, scorched hulk useful only as scrap. Outside of such large engagements, it is most suitably used for ambushes, where it's speed is less of a hindrance, or as a rear-guard artillery vessel, meant to fire missiles at the start of battle at planned targest that will collide with the enemy just as it's shields are broken, assisting with laser and EMP support as needed.
The largest ship of the group, the Spearhead Heavy Cruiser, more than twice as large as the Crescent Corvette, is truly designed with great battles such as this is mind, with large stocks of ammo, enough for 8 volleys, more than enough for them to find and rip apart the smaller and weaker of enemy ships, as they were designed to do, changing targets if their original is slain. It is meant for and easily can engaging multiple targets simultaneously, boasting 12 pulse cannons and the customary pair of lasers that can batter ships into oblivion, put together with their launch rails. But their true strength lies in their durability; bulkheads and heavy plating beneath their weapons means that the Spearhead is quite difficult to put out of commission, even once disabled, and it's formidable array of shields, generators, and overcharge batteries, also twice that of the Crescent Corvette, puts conventional assault to shame. An intimidating vessel, with good reason, the Spearhead is, in the end, meant to draw enemy fire away from it's more vulnerable companions, punishing enemies who seek easier targets with the newly freed power flowing to it's pulse cannons. The best way to deal with such a vessel, of course, would be to use railguns or other similar weapons to strafe it's flanks and front, ruining offensive capability before ignoring it once the majority of it's armament has been destroyed in favor of easier targets. Or, if one can maneuver in such a way, to take it straight from behind, blasting through the primary engine block to break into the condensed area, a weak point even surrounded by armor as it is, containing it's shield, power, and overcharge centers, subverting most of the ship's equipment entirely(presumably, engines would be easier to destroy than armor, yes?).
Also, can we target/scan multiple ships in one turn?