Hi, David. Here's what I can answer.
Low-light af is poor with all lenses, even fast primes. It is a weakness of the camera.
Center-point autofocus gives you better control over the point of focus. I consider multi-point to be primarily a marketing gimmick, and for inexperienced users.
The DA 16-45 is sturdy enough, and is superb optically -- one of Pentax's best zooms ever. Shoot with it and you will learn to overlook its physical design.
Joe
