Ship scratchpad side notes
Names / sizes
Capital/Light ship 'class names' are the hull sizes, the role is NOT fixed, the descriptions are just suggestions/typical ideas, it's just that each hull size has different base bonuses to speed, structure and of course different amount of space available for components.
There's no simple 'battleships do +25% damage to destroyers' rule, but there is a 'battleships can take 25% more damage than cruisers (course the cost balances this) and they can fit heavier weapons, so a typical battleship will carry weapons that do 25% more damage' result, which produces similar effects without the nasty boringness.
What that means is that players are guided into the roles envisaged, but not straight jacketed by them. Although the role of a ship is determined by the components not by the hull size, but the hull size will place real considerations on what kind of roles work well and what don't. I'd call it "constrained design freedom".
e.g. The largest hull size 'battleship' would a pretty hefty penalty to speed, so nobody is going to try and use it for a fast interceptor ship, 'cos it won't be, no matter how advanced the engines you stick in it. However it does have large internal space, so you can fit it with the larger weapon mounts, meaning you can do some real damage, and it has a good multiplier to structure, meaning it can take a lot of punishment, so fitting it with big weapons, heavy armour and using it in a classic battleship role would a typical idea. Alternatively you might want to use all that hull space to fit it full of missiles or fighters, and build a super missile ship/carrier since as you'd have great range, the lack of speed wouldn't matter.
Equally the really small ships (frigate/corvette) have low structure and armour multipliers, but good speed multipliers, so using them as sit-still bruisers is a waste of their advantages, and anyway they haven't the space to fit decent heavy weaponry. What you could do it go the standard route, and fit them with light weaponry, good engines and use them to chase down undefended stand-off groups, or you could cut the engines down and go for even more light weaponry and use them for point defense boosters for capital ship groups, freeing up space in them for the big weapons.
The mid sized ships (destroyer/cruiser) are the most flexible, and the areas where the player has the most opportunity to develop their own strategies, go the usual route and use them as progressively slower but better armed ships, or fit them with a bit of ranged weaponry and use them as long range hitters that can stay out of range, or any of a million other choices, the point is that by setting weapon sizes right, and by scaling survivability and speed with hull size, we set up an arrangement where we can feel happy that most ways a player tries to go with a design will give them more options and fun, but will also leave them open to some kind of counter, or will give up enough of the ships natural advantage that they will have a hard time against someone who simply 'plays it straight' unless they're tactically brilliant.
So, you can't build 'tiny battleships' or 'big corvettes', because battleship/corvette are names for the hull sizes, not necessarily the roles. However you could build a battleship sized ship you try and use like the suggested use of a corvette ,and vice versa, of course it'd probably be crap, 'cos it'd be slow AND weak, but if you can find a tactic that exploits it (maybe it's simply unhittable by ranged stuff because of all that pd?) then why not.
And you CAN build ranged ships of (essentially) ANY size, which is why they aren't listed by size (though I suggest the smallest sizes simply not be viable (i.e. you can' fit the launchers/fighter bays int, so it has to be frigate or maybe destroyer at least.), and it's up to the player to decide which sizes he feels best fit his strategy. This is since so long as there is a reasonable speed penalty for carrying stand-off weapons, i.e. they aren't actually fast enough to escape the equivalent non-stand-off ship, I can't see whether you choose to launch your missiles from one big ship or several smaller ones making a lot of difference. That'd all be down to the player's personal choices about eggs-in-one-basket arguments, survivability, ammo levels vs. fire rates etc..
Content creation considerations
Medium - long term I'd quite like us to use different models for stand-off ships than conventionals of the same size, so for that reason alone it might be worth aiming to only use a subset of the hull sizes for stand-off ships, i.e. to limit the work required of the modellers/artists. I think there should still be a good range though, so that players can use stand-off weapons at a good range of tech levels, buidling smaller missile ships early on then progressing to larger ones later.
As for v.4, I agree we'll need a simplified, cut-down version of this framework to get something up and running quickly. I was aiming for the existing mark ships to be reused to cover the key parts of it, so that the tech tree, models, graphics don't form a bottleneck, and other ships classes can be slottd in when we want.
I'd suggest using the mark I as Corvette, the II as a destroyer, the III as a destroyer/cruiser sized missile ship, and the IV as a dreadnaught/battleship. I think that allows the player to explore the core of the interconnections, whilst minimising our immediate work, and allowing the rest of it to be built up slowly.
tech development sequence
As for the tech line development, I was thinking that it works well if the hull sizes are unlocked progressively, as the player would then have to adapt their fleet configurations to the newly available ships and opponents as bigger classes with their differing capabilities were developed, redefining the role of older classes.
Since Stand-off (IF) weapons are just normal weapons components, you can fit them to any hull size they'll fit in as soon as you develop that hull size, there's no need to research a separate line of hulls for stand-off weapons (silly me, what was I thinking...)