So as I understand it, the Mycenaean civilization went away sometime around 1200-1100 B.C.E. After that we know nothing about what really happened in ancient Greece until around 900 B.C.E. where we have the Dorians fully established in western Greece and the Peloponnese. At this point we would have Sparta and others fully established and the Spartan Helot/Perioikoi system fully in place.
During this dark period we would see a transition from the proto-Greek Linear A/B script, to something recognizable as Doric/Attic/Ionian Greek.
During this time we would also see a decline (as I would call it but most historians would hesitate to call it more than a transition) from Mycenaean/Minoan art to the Geometric Period, skipping over the proto-geometric period of Greek art.
Does this sound correct or do I have something confused?
Your timeline is not too bad, with the following provisos:
Dorian migration: there's no consensus on whether it makes sense to talk about a historical "Dorian migration". Purely in terms of number of voices, the weight of existing discussion leans against it. But it's by no means settled. Linguistic arguments often take it for granted that West Greek dialects in the Peloponnese, including Doric (but not including Arcadia, in the middle), were an overlay over an earlier dialect or dialects; but on the other hand we can't know for certain that proto-Doric wasn't already being spoken in the Peloponnese during the Mycenaean era.
Sparta: no way was the classical Spartan constitution in place by 900. Sparta was just a village at that point. It may possibly have become part of a two-headed regime alongside Amyklai, but that's still very local. It's likely that Lakonia subdued Messenia to the west in the 700s BCE; Sparta also started sending out colonies in the late 700s. It's in that context that we start to hear reports of Spartan perioikoi and helots that are vaguely plausible. But even for after that date, the information that's reported about Sparta's political system isn't at all trustworthy until we get to the latter 500s.
Script: it's not right to talk about a transition from Linear B to the classical/modern alphabet. There was a gap in the middle of about 400 years of total illiteracy. Linear B was abandoned altogether ca. 1180 BCE. We have no evidence of the classical/modern alphabet until after 800 BCE. There is some debate over how gradual the adaptation of the Phoenician alphabet was, but no actual evidence to put it earlier than 800. Even after 800, for a long time writing served as a way of making vicarious utterances (e.g. "I am a nice drinking cup", "I am the grave of so-and-so", texts directly addressing the reader of the text), rather than for impersonal records: we don't have clear-cut evidence of writing being used for archival purposes until the latter 500s. (Though many people -- I suspect mostly literature people, rather than historians -- would like to assume that it was used that way considerably earlier.)
Art: a more gradated set of phases is probably advisable: Mycenaean (down to ca. 1180 BCE), Sub-Mycenaean (to ca. 1050), Proto-Geometric (to ca. 900), Early Geometric (to ca. 800), Late Geometric (to ca. 700), but with lots of leeway on those dates for different places, different styles, and whopping big grey areas between them.
I'm jumping in way over my head here, but I've been interested in this for a while now. My take on the situation, which I'm offering for correction if I'm wrong, is as follows:
There is no doubt of the existence of the various Greek dialects, and these were in place well before 500 BCE or so. It seems clear that there were communities/states that self-identified as 'Dorians' and were recognized as such by other Greek communities. However, the Greek dialects were mutually comprehensible and can't be considered as separate languages, and it seems that the Dorian, Ionian, Attic, and Aeolian communities had more in common than otherwise: they all went to the Olympics, to the same Oracles, had the same general kind of cult practices and social customs, etc.
So it seems to me that notions of a Dorian Invasion/Return of the Heracleidae evolved as a post-facto attempt by later writers of the Classical age to explain the state of Greece as they found it rather than a continuous transmission of any actual events. As a modern example, let me point to the Doric dialect of Scotland - there's no doubt that there are real differences in speech patterns, but I've never heard anyone posit that they are the result of an invasion.
So, is this a crazy idea?
I thought that this was interesting:
http://www.dartmouth.edu/~prehistory/aegean/?page_id=615
And this goes into the Dorian question pretty thoroughly:
Only offered as possible further reading.