Ultimate question: Why anything at all?

I see here people trying to apply logic to as yet ill defined concepts and without any agreement on postulates.

Let me point out that logic can only take you from one logical predicate to another via implication. You will get no answers to the question of "why" this way. Deduction will only answer questions of the logical consistency and logical equivalence of sets of statements.

In order to define nothing, you need to define its complement with respect to 'all that is'.

So in this regard, you need to know what nothing is to define what everything is which means that nothing in whatever form it is in needs to having some kind of interpretation in order to really and truly analyze what is being described and its implications.

Proof:
Suppose non-existence
then nothing is something
and nothing is not!

I have some good news for you - since nothing cannot be, it follows that non-existence cannot be as well. We are all eternal!

I didnt think you would notice

Death IS not: You will never notice you are dead.

to exist is but another word for to be..."exists" = "is"

But I have noticed quite a few people's deaths. This is rigorous enough for me as a confirmation that death is/exists. Death is one of those very few things that you are 100% certain that exists.

I've been thinking for some time that reality might be better characterized as 'what remains after you set some constraints on everything [1] and then quotient everything else away'.

In this picture the focus shifts from 'things' to the constraints (which are relational, by the way), and I think it is not only a metaphysical issue but something to be taken into account when building a modern physical theory (some of these ideas are present in some works, but not so mainstream I'd say).
What the constraints are and where they come from deserves another discussion.

Anyhow, I am curious about 'the Peircean view that [reality] self-organises out of vagueness via semiosis', can you provide some specific references please? I was not aware of this at all.

Peirce's cosmology, or "mathematical metaphysics" (CP 6.213) aims to show "how law is developed out of pure chance, irregularity, and indeterminacy" (CP 1.407). The account, outlined in the accompanying chart, unfolds as follows.

“If we are to proceed in a logical and scientific manner, we must, in order to account for the whole universe, suppose an initial condition in which the whole universe was non-existent, and therefore a state of absolute nothing.. . .But this is not the nothing of negation. . . . The nothing of negation is the nothing of death, which comes second to, or after, everything. But this pure zero is the nothing of not having been born. There is no individual thing, no compulsion, outward nor inward, no law. It is the germinal nothing, in which the whole universe is involved or foreshadowed. As such, it is absolutely undefined and unlimited possibility -- boundless possibility. There is no compulsion and no law. It is boundless freedom.”

Now the question arises, what necessarily resulted from that state of things? But the only sane answer is that where freedom was boundless nothing in particular necessarily resulted.

“ . .I say that nothing necessarily resulted from the Nothing of boundless freedom. That is, nothing according to deductive logic. But such is not the logic of freedom or possibility. The logic of freedom, or potentiality, is that it shall annul itself. For if it does not annul itself, it remains a completely idle and do-nothing potentiality; and a completely idle potentiality is annulled by its complete idleness. (CP 6.215-219)”

Thus the principle that the logic of the universe is at least as sophisticated as our own -- that it therefore includes retroduction or abduction, the spontaneous form of inference that initiates a stream of inference -- leads us to an account of the first stirrings of determination in the utter indeterminacy of Nothing. This is the first appearance of a mode of positive possibility, different from the mere absence of determination that characterizes the initial zero-state.

“I do not mean that potentiality immediately results in actuality. Mediately perhaps it does; but what immediately resulted was that unbounded potentiality became potentiality of this or that sort -- that is, of some quality. Thus the zero of bare possibility, by evolutionary logic, leapt into the unit of some quality. (CP 6.220)”

The potentiality of a quality, in Peirce's metaphysics, is analogous to the Platonic Form or Idea, in that it is a timeless, self-subsisting possibility that serves as the metaphysical ground of the world of actual existence.

“The evolutionary process is, therefore, not a mere evolution of the existing universe, but rather a process by which the very Platonic forms themselves have become or are becoming developed. (CP 6.194)”

http://agora.phi.gvsu.edu/kap/Neoplatonism/

I skimmed through it, and some parts are serendipitously close to a post about the emergence of the laws of physics and their co-evolution with the universe (linked to Davies, Wheeler, etc.) I had half-written and I wanted to submit to this forum - at this point I am not sure I need to post it any more.

But I have noticed quite a few people's deaths. This is rigorous enough for me as a confirmation that death is/exists. Death is one of those very few things that you are 100% certain that exists.

I have some good news for you - since nothing cannot be, it follows that non-existence cannot be as well. We are all eternal!

So, why anything at all ?

My view is that the concepts "Nothing" and "Something" are primitive.

“Being” seems to be both “immediate” and simple, but reflection reveals that it itself is, in fact, only meaningful in opposition to another concept, “nothing.” In fact, the attempt to think “being” as immediate, and so as not mediated by its opposing concept “nothing,” has so deprived it of any determinacy or meaning at all that it effectively becomes nothing. That is, on reflection it is grasped as having passed over into its “negation” .

Thus, while “being” and “nothing” seem both absolutely distinct and opposed, from another point of view they appear the same as no criterion can be invoked which differentiates them. The only way out of this paradox is to posit a third category, “becoming,” which seems to save thinking from paralysis because it accommodates both concepts:
“becoming” contains “being” and “nothing” since when something “becomes” it passes, as it were, between nothingness and being.

That is, when something becomes it seems to possess aspects of both being and nothingness, and it is in this sense that the third category of such triads can be understood as containing the first two as sublated “moments.”

http://plato.stanford.edu/entries/hegel/

Why anything exists at all is a somewhat religious question and i am afraid can only be 'answered' within the bounds of religion, i.e. not here.

Looking for an answer to the question "why there is anything rather than nothing" is, in the strictest sense, a nonsensical question. Observe that merely asking the question "why there is anything" always perceive (recognizes) there is something to begin with. Except for sentient beings of whom "why" questions can be asked, only "what" and "how" questions are relevant to things (and processes) that exist in the universe.