There aren't any good sources for spining short arrows like there are for longer arrows. You will have to experiment and spine your arrows by shooting. When you find one that shoots perfect, then you can duplicate that arrow. However, even when you think you have all the characteristics duplicated, some of the duplicate arrows will not fly as well as the first one. That's OK. Just make sure you've made enough to give you a good set of arrows that will work to your satisfaction.
As for arrow speed, there are many factors that I can tell you about that will help make your arrows fly faster but some of the hints will not work because every bow is different. In general, arrows that extend past the bow at full draw will be easier to shoot accurately, especially at 24" draw and under. Also, a low brace height will give your arrows more speed but you'll need to protect your wrist from string slap.