That being said, I highly recommend it, but to be used with caution.
By the way, if you take this drug, you will notice your urine will smell differently (different chemical composition). That (logically) means that your body either retains something it should have gotten rid of or the opposite, meaning your are changing the chemical composition of your body. Science has no idea how this drug actually works (we only know that there is some kind of effect) and has no idea what its long-term effects are.
A change in the chemical composition of urine strongly suggests a change in the body, but doesn't "logically" prove it. In the simplest case you could imagine consuming some kind of dye which is simply excreted and not metabolized, which could change the appearance of your urine, kind of like in
https://en.wikipedia.org/wiki/Beeturia
(where the urine change itself mainly reflects what the body did not absorb).
Another possibility is that the body breaks down the drug and excretes all of the reaction products. In principle, that could occur without consuming any other substance, just by applying energy to cause a reaction to occur, or by providing a catalyst.
Also, some chemical changes in the body are beneficial (though the typical random change is most likely not).
By threshold dose I mean take no more than is needed to get an effect. I experimented a bit and found 50-100mg of modafinil (1/4 to 1/2 pill) to be effective and have never taken 200mg.
Escalation on tolerance is the exact opposite of what you want. On the first hint of tolerance, stop. Again think about the control system at work. Your body is trying to maintain homeostasis, which is usually a very good thing.