Almost all of our difference of opinion stems from this:
How else ought they be interpreted? The problem I see is that it is written is very explicitly. "Whatever is natural is easily procured and only the vain and worthless hard to win." And also, as we discussed a while back, PD3: "The magnitude of pleasure reaches its limit in the removal of all pain. [...]" It is very difficult for me to interpret this quote in any other way than what is explicitly stated. That is, when all pain is removed, that state of ataraxia and aponia are the LIMIT with respect to pleasure. I can't conceive of this in a way somehow allowing this to NOT be the limit, unless something is to be said about mistranslation, or a hole in the principle doctrines. Or even that certain modification is necessary.
I will not say you are wrong, but I will say that I interpret things very differently because while the sentences you quote taken separately are quite clear, they do not stand alone, and they occur within a definite context which in my view prohibits the conclusions you think are clear.
The context in my view is that long before these positions would have been stated, Epicurus had previously stated that there are only two feelings, pleasure and pain. He had also previously stated, in PD3, that the limit in QUANTITY of pleasure is the absence of pain. Everything must be interpreted in that context, and within that context, whatever is not pain is by definition pleasure, and whatever is not pleasure is by definition pain, and the quantity of absence of one is ALWAYS the quantity of presence of the other, by definition. And that means that when one goes to zero quantity, the other goes to its limit of quantity, by definition. However this is only a definition of QUANTITY, which Epicurus is careful to state in the beginning.
So yes, zero pain is the "limit" of pleasure, but only in quantity, and not in any other respect. If it were not necessary for us to take other aspects of pleasure into account, we could by definition live the best life possible by killing ourselves, or drugging ourselves comatose, because in both cases that results in zero pain. That would be a perverse result, but that is exactly the result that is produced by reading these texts in isolation and not seeing them as part of the whole. A whole in which "Wherefore we call pleasure the alpha and omega of a blessed life. Pleasure is our first and kindred good. It is the starting-point of every choice and of every aversion, and to it we come back, inasmuch as we make feeling the rule by which to judge of every good thing" and "I know not how to conceive the good, apart from the pleasures of taste, of sex, of sound, and the pleasures of beautiful form.”
The same thing goes for the sentence that when we have no pain, we have no need of pleasure. Taken alone that seems clear, but it does not mean that suicide or being comatose is the best life. Viewed from the perspective of quantity, any Epicurean who sees that pain has been reduced to zero also knows that it has been reduced to zero by filling the human experience completely with pleasure, so as to drive out all pain. In Cicero's phrase, "Nothing is preferable to a life of tranquility crammed full of pleasures."
Or, in the words of Torquatus: "Let us imagine a man living in the continuous enjoyment of numerous and vivid pleasures alike of body and of mind, undisturbed either by the presence or by the prospect of pain: what possible state of existence could we describe as being more excellent or more desirable?"
And in this context, natural and necessary also is seen not to be a call to the "zero life" but simply the observation that some things in life require a lot of effort, and some things don't, and that in general those things that require a lot of effort entail at least the possibility of a lot of pain. But if you keep in mind that the goal is pleasure, and not the zero state of absence of pain, then this observation is nothing more than a part of the analysis that before you choose to do something that entails a lot of effort, you better be sure that you will in fact get a lot of pleasure, and you better be sure that you do it in such a way as to minimize pain. Flying to the moon requires a lot of effort but can be done safely with a huge investment in modern technology, and therefore can be viewed as a tradeoff that is very worthwhile. But flying to the moon without proper preparation is going to lead to great physical pain and perhaps death, and so is not to be undertaken lightly.
So in sum each of the quotations that appear in isolation to call for a minimal life can be seen to not call for a minimal life at all. Did Epicurus live a minimal life by surrounding himself with a philosophical school of people, churning out books, running a household with many slaves and, and leading a philosophical revolution? Did Lucretius pursue minimal living with the Herculean effort of his poem? Of course not - they saw their lives as short and precious, and needing to be filled with the activities that would bring them the most pleasure while at the same time pursuing that pleasure in a way that would cause as little pain as possible. But they certainly knew and welcomed the pain that would be required in their effort, because they knew that the pleasure that would be produced was well worth it.