You might want some sort of graphics program to make your sprites. POVRay is generally highly recommended among the artists here. It's free, will work on practically any system (Mac, PC, Linux, Unix, etc...), and is a small download. Unfortunately, it has a somewhat high learning curve. Strata 3D, or Infini-D have shorter learning curves, but they aren't necessarily free, and might not work on slower systems (I don't know). Lightwave is what ATMOS used, but it's almost prohibitively expensive for the average weekend modeler (same goes for Maya, SoftImage, 3DSMax, etc).
You might want a raster paint program like Photoshop to make your textures, and to touch up your graphics.
I'd suggest making a mission tree so that everything is planned to the last detail.
Getting a program to check the spelling on your descs is VERY important because players won't take you as seriously if your plug is riddled with spelling and grammar errors.
Also, you should plan out stuff in the order that they need to be done. For instance, you can't make the outfits until you have the weapons. You can't make the ships until you have the weapons and the governments. You can't make pers, dudes, or ships until you have the ships. You can't have systems until you make the spobs. You can't make the spobs until you've made the fleets. You can't make the missions until you have the spobs, etc. Be very careful to plan this out so that you don't waste time. (If only I had followed my own advice)
Matrix
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"Nothing is fool-proof to a sufficiently talented fool."
