Step 3: Because I knead the dough
Back to business, though. After you've come just about as far as you'll get with stirring, switch to kneading. I keep the dough in the bowl at first because it's very un-homogeneous and I don't want the buttermilk running all over the place. When kneading in the bowl, I notice that most of the time a bit of the flour will remain seperate from the dough in the bottom of the bowl, so when I switch to kneading on the table top, I use that to keep the dough from sticking to the table top. This is an important step: Always dust the table top with a little flour (1 - 2 table spoons), or the dough will stick to it, making it very difficult to knead it.
The feel of the dough should be warm, a little moist, but not sticky. Rule of thumb: If too sticky, gently add (one table spoon at a time) flour. Most of the time, 2 or 3 table spoons do the trick. If too dry (dough won't come together, stays in crumbles), moisten your hands a little with water, buttermilk or milk, and go on kneading, repeat if neccesary. It doesn't work well to add liquid to the dough in any other way, in my experience.
Okay, at one time or another then, you'll come to the point when you have the right dough texture. This means it doesn't stick to your hands or the table top and you can knead and handle it quite comfortably. From this moment on, you knead for structure. The more wheat flour in the dough, the longer you should knead it. This activates the glueing components of the wheat flour (which is whwat gluten is, by the way), improving the structure of the bread. Normally, I knead vigorously for about 5 minutes after I stop adding things to get the right texture.
If using a rye-containing mixture, you can reduce that time by about half, because rye flour's glueing components don't need to be activated that much. I don't know about buckwheat or spelt flour, but with my 5 minutes of kneading I get nice results.
Listen to you hands: they should tell you that the feel of the dough changes a little during this kneading process. It should get even less sticky and soft/firm at the same time. A bit like play-dough after you handled that for a while. It's hard to explain, much easier to feel for yourself, so go experimenting!