I am glad you are being entertained by our doctrinal lucubrations -- it's an
ancient and revered form of Buddhist mental gymnastics to stop the brain
from ossifying :)
I would be happy to recommend a few books and articles which should get you
started -- that is, on your research; the gymnastics are an optional extra.
You will, of course, find that many orthodox Theravadins will deny that
there was any historical development of the Pali canon,since they believe
that it was all spoken by the Buddha during his lifetime (with a couple of
obvious exceptions). Approaching Buddhism from a strongly faith-based
position, they are perfectly entitled to that opinion and are free to, and
generally will, ignore any evidence to the contrary.
As for attempts to stratify the Nikayas and Vinaya (leaving aside the
Abhidhamma), the problem is methodology and preconceptions. For example,
stratification can be done on philological or doctrinal grounds, but often
scholars will then proceed based on their unspoken or even unrecognized
assumptions. The one book I recently recommended here is Tillmann Vetter's
Ideas and Meditative Practices of Early Buddhism (Brill 1988?). It is a
very slim book but packed with important insights -- you would do well to
read it several times. He does not deal with textual stratification per se,
but rather doctrinal stratification. His conclusions will horrify
faith-based practitioners though they provide a template for stratifying
texts.
The development of the Nikaya schools in India is also extremely complex as
much of the surviving material that decribes the emergence of the various
schools tends to be contradictory in one way or another. The standard work
on this is still Bareau (hop you can read French). Some of Hirakawa's ideas
are indeed now regarded as outdated, especially his views about the
emergence of Mahayana, as you surmise. Lamotte's book on Indian Buddhism is
still highly regarded and is now available in English.
Here is a short list of books and articles you might find useful in addition
to Vetter mentioned above:
The only book I have seen which attempts a detailed textual stratification
is
G.C. Pande, Studies in the Origins of Buddhism (Motilal 1974)
For doctinal stratification:
Lambert Schmithausen, "On some aspects of descriptions or theories of
Liberating Insight and Enlightenment in Early Buddhism" in Studien zum
Jainismus und Buddhismus, Franz Steiner Verlag 1981 pp199-250
Johannes Bronkhorst, "The Two Traditions of Meditation in Ancient India",
Motilal Barnarsidass 1993 [This is the 2nd edition, which you should try to
get]
Also try to find Gombrich's "How Buddhism Began" for a different
perspective and the German scholar von Hinuber has recently written a very
detailed book on Pali Literature (in English, whew).
There is also Frauwallner's important study, "The Earliest Vinaya" (ISMEO
1958), which covers both the textual history of the Vinaya and the Nilkaya
schools.
For Nikaya history there are these recent articles by Lance Cousins:
"The Five Points and the Origins of the Buddhist Schools" in The Buddhist
Forum vol II (1991), pp27-60
"Person and Self" in Buddhism into the Year 2000 (1995) pp15-31
"On the Vibhajjavadins - The Mahimsasaka, Dhammaguttaka, Kassapiya and
Tambapanniya brances of the ancient Theriyas" in Buddhist Studies Review 16
(2001) pp131-181
Better still, if you can read French, try Andre Bareau's Les Sectes
Bouddhiques du Petit Vehicle" (BEFEO 1955)
I hope this gets you started. If you want to contact me off-list later for
further information or opinions, pls do so.