Animations?
I don't think so. At least the basic .X animations won't play in the game (I've tried, it just displayes the last frame). Well at least in the ship editor and the galactic map that's the case. Like Kalin said, there are animations in the battle simulator. That's not something I've tried yet, so it might be possible.
Additional Hulls?
Sure. Add your ships, give them unique hull names (ie S0_Cargo_3) and in the GC2Types.xml file add another Hull, fill out the attributes you want and have the Model and Thumbail your new model and graphics.
size and poly count?
I don't know how the engine scales units on the galactic map.
From about 300 units on up to about 1000 units long seems to work well for me in the ship editor.
I recall some one from stardock saying they tried to keep hulls under 2000 polygons (triangles I assume), with hulls that are more prevelant (like tiny or small or cargo, things you'll have lots of in the mid to late game) coming in well under that. Of course StarDock was targeting an 800mhz CPU and generic 32mb DX9 video card as their hardware. If you want to look more at some high performance hardware, several times that at least is feasible. StarDock has said the engine has no built in polygon cap - if you want to make a 100,000 polygon model you're free to put in the game. (And watch your 7800GTX grind to a hault...)
Mount points: as many or few as you like. The more points the more jewlery and components you can add and the greater freedom players have to customize. With fan art ships (like Trek, Star Wars, whatever), you many not want jewlery stuck all over the place as the base model itsel conveys the intended look of the ship. A few mount points for required components may be all you really want.
The nose of the ship should be pointed along the positive Y axis.
An SDK to allow us to modify game rules would be a welcome gift from StarDock. But I have not heard anything regarding the release of an SDK, and a release of the full source would be years away if ever. Modding and this community seems to be more in StarDock's eyes than it was with GalCiv1, but the original never had an SDK released, and StarDock has opted (so far) to not release the source to that title.
