This MaxforLive device lets you randomize tempo, time signature, scale and root note of your set. The latter two for now only work with Push and Ableton Live Beta 10.0.6b1!
Put this in your default template (preferrably on the master track), set the range of the tempo, activate randomization with the buttons to the right and save your template.
On the next start the chosen parameters of your set will be randomized. When you save a set it will not trigger another randomization on loading unless you activate randomization again before you save it.
Or you could randomize the parameters instantly with the buttons on the left.
Furthermore you can have the parameters initialize to settings of your choice with the push of the "Initialize" button.