low-intensity versions of the things you plan to practice are not bad for warm-ups at all. unsoku is good, as are slow repetitions of sen, un, hen, nen, and ten basics. the most important thing is to make sure that the body is fully prepared before doing anything that requires a lot of exertion.

w/r/t stretches, i agree that short holds are probably not going to do much harm, but i would still tend to keep the holds closer to 5 seconds than 10. the thing is, these static stretches are shown to be much more effective for increasing flexability when performed later in a workout. that, and dynamic, moving stretches progressively condition the nervous system to release the residual tension in our muscles. those points taken together constitute my reasoning for suggesting dynamic warm-up and statics cool-down stretching.