I would like to improve my efficiency in kneading & stretching the dough, lest time constraints prevent me from continuing with this innovation. I am thinking about using, say, a Kenwood Chef device with a dough hook to help me. Is there any reason why I should not do this?
Could I use a whisk attachment or similar to improve the smoothness of my white and rye mothers?
The Kenwood will do an excellent job on developing the breads and because you have started life out developing the dough by hand it will be easier for you to asses when the dough is fully developed by the mixer.
The beater would be the tool to cream the Mother when you are feeding it, although this may make more work for you in washing up, as it is often quicker and easier just to add the flour and water to the tub and just stir together roughly letting the process take care of the rest.