Don's questions are great, and Godfrey's short reply is too. Mine is early in the morning and necessarily going to be short too, but here's a start, focusing on one part of Godfrey's answer:
But my take is that Epicurus was dealing with theorizing, as he didn't have the technology to verify many of his conclusions.
Epicurus didn't have the technology, and Epicurus (nor any single man) didn't have the time, to put in an unending 24/7 exploration of all of natural science.
And here's the big point:
NOR DO WE! Nor does ANY individual person!
And yet we must live, and yet we need a single overarching perspective which allows us to organize our lives, and not live in fear from moment to moment that we are totally wasting our time because we are not on our knees before god, and not facing eternal damnation in hell, and not hopelessly doomed by "fate," nor blindly needing to follow some ideal form that would condemn us to needing to acknowledge the concept of "a horse" without ever being confident that the large animal with hoofs and mane and tail in front of us is actually a horse.
Before I read these comments I was going to say that I was confident that Epicurus, if he had the opportunity, would strap himself into a spaceship and be among the first to blast himself off into space, because he clearly had that kind of drive to know more so that he could improve his understanding of nature.
But we need to realize that that might NOT in fact be what Epicurus would do, if he were alive today. He might look at the risks and benefits of space travel and decide that as for himself, particularly depending on his health and his age and his likelihood of return, that it was more satisfying for him personally to stay here on earth and, using whatever time and resources were open to him, to improve his philosophy and share it with his friends and gain enjoyment from that while acknowledging that his choice would forever deprive him of personally seeing (for example) the other side of the moon.
Does everyone have to devote themselves to being a physicist in order to make the best use of their lives? Certainly not. But how do we are they have confidence that we are "making the best use of our lives"? These are philosophical issues (questions of epistemology, and ethics, and the study of nature) where we cannot demand "perfect knowledge" before having confidence in our answers, because "perfect knowledge" is NEVER available to ANY of us, nor will it ever be so long as mankind continues to exist.
What we have instead are our canonical faculties - the senses, feelings/affections, and anticipations/preconceptions, and we judge our success at life by how well we use those, just as we judge a dog or a cat by how well they employ their own natures as dogs and cats. We can't / shouldn't hold ourselves as humans to a higher standard than we would hold any other living thing, but that is what is going on when we look for "perfection" and criticize anyone who has confidence in their decisions on how to live life simply because they are consumed with doubt because they don't have "perfect and complete knowledge of everything."
We don't have that, we never will, but we need a philosophy for living now in our current state of less than "perfect" knowledge. That, it appears to me, is the direction Epicurus is pointing.