Using an opiate as potent as hydro - although in my view, using ANY opiate - 3 days weekly is way too much. It could conceivably work in the case of someone who doesn't care either way whether he can get high or not, or in the case of someone who is simply thrown in the direction of opiates by chance, but you're very clearly not this person!
Two things really jump out at me from your story: 1) The attachment you have already developed for opiates; and 2) The fact that you're using not purely for fun but to enhance the quality of your life, because you're not getting enough pleasure by the usual means.
In my view, 1) and 2) lead so consistently to drug addiction that it's almost childish to consider the possibility that they won't.
I remember constructing such elaborate plans to regulate my use when I discovered oxy. I'm talking literally 5-page manifestos that took me hours to draw up and included all sorts of regimens and accounted for all sorts of prognoses. I think that when a person feels they need to give serious thought to their use, they are at a turning point, and probably already well on the way to addiction.
Not that it really matters, because it is virtually impossible to get through to a person in this state! Honestly, did you want this sort of advice? Or did you want to be told "yeah, go for it"? Drug addiction is powerful and insidious; it takes an equally powerful and unwavering sort of honesty and self-examination to beat it. That is, to view it in the present for what it is, and not in retrospect and after the damage has been done.