I appreciate you sharing this, particularly as it looks well-considered and provides references. Like /u/parolang, I notice some tensions with stoic teachings that may be interesting to explore.
One question I would ask which regards your Epicurean leanings is, how confident are you that the emotions can be accurately categorised as positive and negative, and, furthermore, how confident are you that the pursuit of the positive and diminishment of the negative is the true path to peace of mind as opposed to the pursuit of virtue (which is the stoic way)?
To provide you with a more difficult case than the ones you cite, how would you approach grief? Grief is uncomfortable. A world without grief might be a superficially happier world, but would it be a better world if we grieved for no one?
To take a more modern psychological approach, there is evidence that humans are broadly similar in their emotional profiles despite wide variation in their personal circumstances (excepting extremes like profound poverty). No matter if you're humble or profligate, healthy or ill, we can only maintain a certain amount of happiness before diminishing returns, and we can only suffer so much before we are numb. This is why I take a focus on the emotions to be essentially aimless as there is only an illusion of control, whereas deliberating about virtuous action is actual control.
The other main point I'd like to discuss is how you situate ultimate responsibility impossibilism in all this, which I think is the most modern outlook of your framework that sits least well with all the other parts (not necessarily a bad thing but I think there are genuine problems).
Now, I completely agree with you about the impossibility of ultimately responsibility, but I disagree that this it is at all relevant to moral philosophy. The equivalence is free will with ultimate responsibility is a false move that merely defines free will out of existence rather than refuting it; yes, ultimate responsibility is impossible, but is it the only possible conception of free will? No, so we have to look at the others.
Compatibilism accepts that there is no ultimate responsibility and accepts that our actions are products of materialist determinism. However, it also gives room for ideas of moral agency, which seems necessary for a moral philosophy likes (y)ours.
There are many arguments for demonstrating this, but I'll take the modern psychological one again. Your regress is essentially predicated on the observation that the mind reduces to the brain. The mind is a product of the brain. This I accept. And, for the sake of the argument that follows, let's remember that this kind of idea is what gives us an understanding of pathologies like substance addiction as 'diseases' - the behaviour is determined by the neurochemistry.
However, there is stark evidence all over the place, whether we're looking at behaviour modification techniques in psychotherapy or analyses of everyday psychology like Kahneman's System 1 and Sytem 2, that it is also the case that the mind alters the mind. What you consciously think and believe in one moment can change what you think the next. For example, in the treatment of addictions, the first, neurochemical story would have the substance user give in to their temptations because of hormone rewards which would have to be circumvented by medical interventions. However, it is also possible for a substance user to consciously deliberate about their actions in order to alter their future actions, requiring no medical intervention at all - the conscious mind restructuring itself.
Now, you could (rightly) point out that even allowing for this, a mind that alters itself is still reducible to a brain. This is true, but we have at least two tiers of complexity here:
In each case, it is necessary that all states of mind are reducible the brain and, therefore, physical law. However, compatibilism says that the second, more complex chain is qualitatively and importantly different. It is what separates us from lesser- or non-sentient animals and gives us a kind of moral agency they do not have. It does not give us ultimate responsibility, but it does give us free will, and this is necessary for (y)our kind of moral philosophy.