I just finished with a fairly comprehensive list of needed art assets for all of the ships and items players will generally interact with.
There are about 600 items on the list (some simple, some more complex).
They represent about 300 hours of artwork, and about 30 megs of in-game art assets (if we utilize channels properly- that's using one byte per pixel to store normal data, another to store colour [using a palette], and another to store alpha [alpha really doesn't *need* 256 levels, but the others can't take more compression than that]), and maybe as few as 15 megs after compression (there will be a fair amount of empty space in the files, averaging about 50%, the redundant data of which should be easily compressed).
This does not account for: GUI, Backdrops (planets and nebulae), particle effects, scenes, or profile images for characters.
The GUI, from what I've seen, can stand a lot of graphical compression for the final release (tiles for the redundant areas), and 50% of it should actually be able to re-use graphics that make up the ships (the background areas made up of plates and lattice from the ships- which will let us easily theme the GUI to match the ship automatically, if we so chose). A meg should be more than sufficient for the buttons, dials, and meters.
We should be able to find ways to systematically generate the background planets and nebulae based on compositing a few simpler images. Luckily, being background images which we probably won't need alpha on (if we use the right forms of colour channel addition when compositing the images) and which we won't need pristine clarity on, lossy compression like jpeg could be an option, bringing us down to, possibly, four megs with the release.
For backdrop scenes, likewise, we can probably compress them; although that all depends on how many we'll have.
With profile images for characters, if we do that, we'll probably want to use something like layering to swap out mustaches, monocles, hair do's, and clothing pieces. Will definitely need alpha there, if we did that, and more full colour depth with people, so any good compression is unlikely. Might be able to do it well with 30 megs.
On the other hand, if we didn't want to bother with customizable profile images (which we very well may not), we could get away with jpeg images at 15k a piece, and make a couple hundred of them for about three megs- which would all have a bit more character as hand drawn pictures (always nice), but would end up being more generically applied. Would be about... 400 hours of artwork.
Throw in a couple hundred hours (and a couple megs) of jpg scenes, and a conservative estimate (with the compression mentioned) would put the game at about 1,000 hours of artwork and 40 megs of graphics in the final release.
How big will all of the music and sound effects be?
How big will the needed libs and the code itself be?
I can only estimate on graphics, but it seems to me that a distribution of 100 megs could certainly be possible.