[Suicide Junkie]

Solid white boxes would indicate that the image location they reference is below the bottom of the planets.bmp
-> You need to increase the height of your bitmap.

If your images are offset by that much, you need to shift them to counter it.
If you used the planetpack bitmap for reference, you probably aligned it to the right, and covered the blue numbering edge with planet images, instead of aligning it to the left.

The order is only relevant to the game for referenceing which planet gets which image. You don't want asteroids looking like stars, for example.

The whole point of the imagemod packs are that players only have to download and install the files once. Since we are talking 60 megabytes of images here, multiplied by however many mods you have, that can add up very quickly.
By using a common set of images, and adding to the end, the BMPs remain backwards-compatible, and have a much smaller footprint on your harddrive.

As for the arrangement of the minis, I did the grunt work there.
It was just Copy and Pasting in paint, using the red & white grid to help align things. Then a renaming of the submitted portraits to match the location of the corresponding minis.