Ah, but the thing is that people come back
because they want more of the same. Not identical, of course, but they don't come back looking for something completely different either.
I don't have the experience or expertise to offer much in the way of advice for the launch strategy. At least a month between releases seems a good idea, but I do wonder whether your free offering (if you provide one) should be your first release - something for people to read when the paid ones come and decide they like your style enough to invest. On the other hand, with the strategy you outline above, you get the chance to evaluate whether you really want to offer one of them for free at all. IF things go well with the first two you may decide it's not necessary. And since it is unlikely that anything will happen quickly anyway, there is probably not much to lose by trying what you have planned. (I'd better stop now, I'm getting dents in my rear end from all this fence sitting.
)