When I wrote Into the Wilderness I had no idea where it would end up. Ten years later I had six novels in the series (and a couple out of it; well over a million words in print). If you had told me that at the beginning, I might have balked. But it all happened gradually, in an almost organic matter.
In my experience the second book is harder than the first, and I think that a second series is going to be harder that the first one, for a variety of reasons. The biggest, for me is simple: this time I know what I’m getting myself into.
So I’ve got one book finished, and I’m launching the second. Maybe better said: I’m sneaking up on the second one. If I look at it directly it runs away to hide in a dark corner.
It is almost like embarking on a second marriage: a long-term commitment that will take a lot of work and make me happy and crazy by turns.