You can take a lot of creative liberty when building ships - don't feel too limited by guidelines. You also don't need to work in 3D modelling software, or even adhere strictly to the scale and lighting angle. You can create great looking ships with rotated vector art, photoshopped NASA images, and there's at least one person out there crazy enough to use
Sleek, aerodynamic bodies with wings do not make much sense in space. Because there is no need to prevent air resistance, ships can be big and blocky with very few ill effects. The upside to aerodynamic designs is that they're visually appealing, and that's a good enough reason as any to incorporate those elements - especially in Corporate designs, where vanity might be a selling point.
Generally, I consider there to be three main components of a ship: The cockpit, the main body, and the engines. Cockpits only need to be big enough to hold a single occupant, and they're a good place to put lights or windows in. Larger ships could have bridges rather than cockpits, which could carry a full crew on them. Cockpits and bridges don't need to be external - on military vessels, it may be wise to keep them entirely internal.
The main body is usually where weapons and devices attach, as well as housing the cargo hold and living space. It should usually be the largest segment.
Engines should be aligned directly with the center of mass of the ship. If multiple engines are used, they should be equally spaced from the center of mass. This doesn't need to be followed strictly - look at the Salvager Nomad, for example - but having a single thruster effect off of the center of mass would look strange and doesn't make physical sense. Torque effects could cause the ship to spin about its center of mass.
Engines are usually very detailed. I suggest you take George's approach here: model one or two really detailed engines and copy them across all your models.
The best way to make your ships fit the Transcendence art style is to look at ships that are already in the game. Taking elements from existing ships is usually fine, but don't go overboard with it. The really detailed cargo hatches in Eternity Port ships and the engines in Vanilla are really great things to look at. Also, it's good to take inspiration from everywhere. Even looking at
Star Wars ships, you can find elements that would mesh just fine with the art style. Even looking at modern and past military equipment is a good idea. Reactive armour on tanks or the glass nose of the Enola Gay may have already found a few places in some models. Even looking at the shape of animal bodies can give good results - I think the Freyr is vaguely sparrow-like.
After some design elements are decided on for a ship, they can be copied across several ships. This is particularly helpful when building sovereigns, as sharing design elements can help to distinguish the ship and help to build new ships faster.
The size of your ship will dictate how many armour segments it should have. Gunship-sized ships, like the three vanilla starting ships, have four segments. Heavy gunships like the Manticore have six.
How much space should there be in the interior? The body of the ship needs to house weapons, a nuclear reactor, living space, cargo holds, etc.
Consider the Hornet's cockpit as the absolute smallest space a person needs, since it was probably built to be as cost effective as possible. Ships that can operate for more than one day at a time probably need some degree of living space. Modern day sleeper cabs on semi trucks are a good starting point - there is enough room up front for operation controls, and just enough room in the back for the driver to sleep comfortably and have a little bit of extra elbow room.
Conveniently, a 53 foot (16 meter) semi truck trailer (the largest legal size in most jurisdictions) has a volume of about 115 cubic meters. If you were to fill that with water, it would be 115 metric tons of water - That's a reasonable size for a playership's cargo hold. For a rough estimate of cargo capacity, 1 cubic meter = 1 ton of mass is a good starting point, but realistically this would be higher/lower depending on the cargo being carried.
So the semi truck analogue holds up fairly well - However, there's still a need to house the other components, such as the engines and reactor. The truck/trailer combination sits at about 15-20 tons, and playerships can range from 30 to 150. From what we can tell in the game, reactors, weapons, and other devices only weigh a couple of tons, so those don't need a whole lot of thought put into them. Engines are the exception, but since the Wolfen sits at 30 tons and has three engines, we can safely assume that those engines weigh less than 10 tons each; You can also expect engine masses to scale proportionally to the ship's mass.
Additionally, ships must be shielded from cosmic radiation (why this doesn't apply to radiation weapons is unknown), must be pressurized to keep occupants alive, and needs a frame strong enough to support multi-ton armour segments.
There's lots of ways to introduce detail into your design. You should avoid having large empty spaces - they're not very visually engaging. You also have to take care that the detail you're adding isn't going to be obfuscated when your ship is put at the in-game scale.
Greebling is one way to "cheat" detail. The best example of greebling is in Star Wars ships. Take a look at Star Destroyers and the Death Star - there's not actually much detail there beyond that. Greebles are usually geometric primitives (like square meshes), but you can also get away with a bumpmapped texture. However, you should aim for having physical details in your ships before resorting to greebling. Other greeble type stuff could include exposed wires and pipes.
Texturing is probably the most important part of all of this. Textures allow for a great amount of detail without adding to the polygon count.
The best way to fit into the game's style is to use George's textures in TransArt, but you'll be pretty limited restricting yourself to just those. Knowing what colours of textures compliment each other is good knowledge to have - try looking at a colour wheel to see which will compliment/contrast. Generally, I'll try using one texture for the main body, and a complimenting texture for finer detail. Adding a complimenting texture to raised detail helps to keep it from washing out during the render.
The in-game scale
The scale for ships and stations is not linear. Here are some common objects at the in-game scale:
Human height (1.8m) : 7.5 pixels (Round up to 8; pixels aren't exactly sub-dividable)
Small Car (4.1m) : 13 px
Semi Truck with 53' trailer (19.5m) : 37 px
Boeing 747 (71m) : 91 px
ULCV Cargo ship (366m) : 277 px
Empire State Building (443m) : 315 px
1 kilometer : 548 px
10 kilometers : 2624 px
Ship and station scale:
size(pixels) = 5 * size(meters)^(0.68)
size(meters) = [size(pixels)/5]^(1/0.68)
Image Rendering Guidelines: http://ministry.kronosaur.com/record.hexm?id=54024
My texture/resource pack: http://forums.kronosaur.com/viewtopic.php?f=5&t=7692
Transart100, George's models and textures : http://forums.kronosaur.com/viewtopic.p ... 101#p56663
Note that TransArt101 is the latest release, but is apparently unavailable.