Hardly a long time, but I did notice you forgone this in recent posts. Much better.
Placeholders are a good idea (I'm using it myself), but only if you expect whatever you're waiting for to be released before you begin "serious" FREDing, or have very accurate placeholders (a case with Inferno, as it had a ton of lo-poly models to work with). Less of an issue with fighters (the "rigging" doesn't have to match physical layout), but with capships turret and subsystem positions, as well as general shape become important.
On the other hand, if you'll be waiting for models, you may end up with your mod suspended ad kalendas Graecas. I had this problem, I've started my mod just when I joined, and I picked it up again about a month ago (still not having all the models I originally wanted, but with enough skill to replace them).