What does a government based on Epicureanism look like?

Yes the reddit abyss is well underway already, when I checked it. I do think it's important to keep in mind that since there is no absolute justice, there is likely not going to be a "best" Epicurean form of society either, and that much will depend on the circumstances then and there existing.

And in addition to the differing views of how to treat people "within" the society, there is the difficult issue of how to treat those outside the society, especially if they would like to come into it, and especially further if they would like to come into it without accepting the full consensus of the original society.

These are definitely difficult issues. Where Epicurus comes in the most, I think, is that he teaches that we need to consider this issue, like every other, in the context of pleasure and pain, and not in the context of abstractions like "virtue." That's a perspective that many people don't like to consider, but if we're going to be rigorous (as we should) then it's the alpha and omega of any ethical question.