Where to put images
If you look in SVN under the most recent version, you'll see a new Expansions folder, with a 1 folder under that. For internal purposes, the expansions will simply be numbered. The parts of the folder structure that will have content in the expansion are all duplicated under the 1 folder, so for instance you have Images and Images\Buy, Images\Ships, etc.
For all of your art relating to the first expansion, those will go in the Expansions\1 subfolders. For anything that is free DLC, that will go in the main folders as usual. The idea is that for anyone who wants the expansion, all we have to do is deliver this one Expansions\1 folder and all its contents, along with a new license key.
The Zenith Remnant Themes
The art in the first expansion, which will be called AI War: The Zenith Remnant, should overall fit with the main game well enough that it looks like all one game. However, that said, the Zenith Remnant art should also all have its own distinct "feel" that explores a few specific themes that are only present in a very small amount in the main game.
The main theme is that of alien technology. The Zenith are a very powerful alien race that apparently have "fallen from grace" so to speak, and are now just a small, tattered remnant of their former empire. Their powerful technology remains, and can be used by the human and AI players as part of this expansion, but some of the most powerful parts of the AI technology ("golems" in particular) have fallen into ancient disrepair and must be rebuilt.
The Zenith are Organic-looking and scary
If you look in the main game at the ZinthStarship ship, that's the baseline image for the new style of the Zenith. Of course, they will need to be developed out far beyond what is there, but that alien, organic, almost buglike look is something I'd like to see carry forward. When it comes to the first of these ships, let's go for some mockups like what you did with the energy reactors, and come up with a new style for them.
Please do note that I don't want all of the Zenith ships to look the same, like different variants on a buglike theme. I want to have a wide variety of visuals here, just as are present in the main game, but this alien theme should manifest itself in ways big and small on all the ships. Some of them might just have a hint of bugishness, others might be completely organic looking in some other but related way (such as, some sort of organic mold or fungus, or some strange flora or fauna that might be related to the Zenith world). We need to think of the entire Zenith ecosystem, rather than just the Zenith themselves, with these sorts of designs, so that there's a clear alien vibe throughout but never a feeling of sameness or monotony.
Core Ships
Some of the ship classes, which are normally just Mark I through IV as you are used to, also will include a Core variant. This core variant is the Mark V version of the ship, the most advanced version that is used by the AI only (and that version should look special/different in some way, not just like a bigger version of the Mark IV variant). My suggestion is to do the Mark I through IV as usual as if that is all there is, and then do the Core version as a secondary initiative almost like it is a new ship class that is tangentially related to the base class.
Golem Ships
This is a new class of ship in this expansion. Basically, these are huge capturable ships that are ancient technology that can only be "brought to life" with a lot of repairs from player engineers (at great cost). Once fully repaired, they become active and let the player wreak some havoc on enemy forces.
Each Golem will have two versions. Inactive, which is basically an old, abandoned, ruined-looking state. They are ancient and in ill-repair. Very colorless overall, and cracked and chipped and broken. Then there is the active state, which is after they have been fully restored to all their glory and are ready to kick some butt. All of these golems are Zenith ships, left over from the Zenith days of yore, when their empire was at its fullest.
