A wise man once told me that time and money are rather interchangeable. If you don't want to spend money on something, spend the time to make it yourself. If you don't have the time, spend the money for someone else to do it for you. Art is a good example. It would be impractical for me to spend the time to produce satisfactory art for the game (my stick figures suck), so spending money is the most efficient route to cover that.
For a good portion of this project, I've had plenty of time. When I started blogging, I was unemployed, and I was not gaming. Then I got a job. Then I got a gaming group. Now I'm working overtime. Time is rapidly becoming a precious commodity. I'm wondering if I should hire writers to work on the rest of the material. Especially with the beast that is Quadling Country staring me down.
On top of that, some "conventional wisdom" in the gaming industry says that your first supplement should follow very soon after (within 3-6 months) so that your fans know your are serious about the project. Some publishers have even mentioned avoiding publishing their game for a time, in order to give the supplement time to be completed.
The trick is, in the highly competitive RPG industry, there's no assurance of success. If the main book turns out to be a loser, why should I invest on a supplement that will just lose money?
On the other hand, marketing is important. My opinion is that the reason so many games fail is due to marketing. This extends to the prepublishing process of market research, as well as the actual promotion of the product. And part of that promotion is creating the impression that your company is not a fly-by-night operation and that the product will be supported. It's one of the reasons I started blogging back in April.
Which brings up the next part of this week's subject: Fluff vs. crunch. For those not in know, these are terms that RPG fans use to delineate rules and mechanics (crunch) from setting information and Narrator advice (fluff). Books that offer solely "fluff" generally do not do well commercially, but that's largely the kind of book that it's going to be. Of course, depending on the material that gets covered, there may be room for more character templates, some spells and magic items, and maybe enough "crunch" to make it worthwhile.