Hi Marcel,
Happy you could contribute something. Although, we may differ in the specifics, I find this statement profound and true:
"For a universe to be operational on logic, all of its constituent must be, although different in appearance, of the same nature because we can't add apples and oranges. Better, it can only work using one cause. This is because no rule of simple logic could decide which of two causes would have priority. All in all, there would be only one type of stuff, only one cause for its spontaneous evolution"
On 'stuff'. What is a stuff? I believe by stuff, you mean substance. What is a substance? Borrowing partly from Leibniz in his Monadology, the fundamental stuff must be of the simplest possible nature, even though more complex substances can exist they will be made of the simplest substance. Now, stuff has properties. What properties can substances have? Substances can have color, mass, charge, taste, smell, size (i.e. extension in length, breadth and width), etc. Of all these properties, which one is sine qua non? Which one is that on which others depend but which does not depend on others? I believe you may agree on extension.
Another way to look at the most fundamental property, is to take a stuff and remove its properties one after the other to exhaustion. For example, take an apple, remove its color, you have a colorless tasty apple. Remove all other removables to exhaustion. What you are left with is an extended object, massless, colorless and tasteless.
On 'only one cause for its spontaneous evolution'. Evolution connotes change. As above, there must be a simplest possible change. The simplest possible change that a featureless simplest possible substance can undergo is a loss of its simplest possible characteristic, i.e. extension. That is, that which used to have size ceases to have size, and that which had no size comes to have size. In short, what exists ceases to exist, and what was not existent comes to exist. I discuss this more in my essay, where I also suggest a hypothesis that: the non-zero dimensional point does not have an eternal existence, but can appear and disappear spontaneously, or when induced to do so..
Best regards,
Akinbo