David,
 
You might want to take a look at my 1983 dissertation, "Directio
Voluntatis:  Ezra Pound's Development of the Long Poem, 1904-1925" (UBC)
 
for some ideas on themes and structures.
age 16 (even before "Redondillas" - 1911).   Imagisme was the conscious
practice of one necessary component for his epic.  He tried to link
imagist poems
into longer forms (sequential poems a la William Rossetti's "Earthly
Paradise" (cf Pound's paradiso terrestre), and the "form" of volumes of
poetry like "Canzoni."  Very few critics have made much of this.  Along
the way in his search for a form for the "long poem," he gave up on
rhymed couplets, Shelley's stanzas, and sonnet sequences, to name a
few.  That is, he EARNED his right to experiment radically by first
experimenting seriously and at length with most conventional forms.
This means that he didn't stumble into the form of the Cantos because he
was incompetent with regular metre, but because he'd gone beyond it.
The "direction of his will" was toward a long poem from the get-go.
2.  Originally, Pound wanted to emulate Dante, and in particular his
tidy tri-partite division, "wrapping up" the intervening centuries.   He
 
admired Dante's "perfect form."  During the 1918-21 period he revised
his thoughts about form  (reluctantly, because his studies had deeply
ingrained in him a love of classical form) to adopt Browning's organic
structure (Sordello) as an antecedent and example.  While living in
France, and to my mind likely due in large part to his beginning his
relationship with Olga (1920-22)?, he continued comparing his own
abilities with the artistic vision of Picabio (ovals, perfect form,
[i.e., Dante]) on the one hand, and  to that of Picabia (wild shots,
epigrams, that expressed "a personality) on the other.  He rightly saw
that his genius was episodic.   So he shifted permanently from his long
ambition to create a "perfect form" in poetry, and accepted his own
predispositon toward creating organic form.
3.  Grass is a wonderfully important theme in the Cantos. (Monte di
Paschi, the mind hanging by a grassblade, etc.)
4.  Look for evidence of his relationship to the Victorians and other
conventional antecedents.  One of his earliest essays compared Flaminius
 
with John Keats!  He wrote a sonnet a day for a year! (burned them!).
So his evident originality grew out of a fully expressed (but not always
 
published) admiration for his conventional, as well as  unconventional,
predecessors.  This conservative aspect of Pound has not received very
much critical attention.
5.  I find it even more useful to think of Pound as an anti-communist
than a fascist.  He was opposed to the concept of levelling down.
Particularly in the area of artistic spirit.   Genius was the only flag
he saluted.  Sometimes he confused the image with reality (Don't we
all?!)  No one cares at all about Dante's politics now.  And I don't
care about Pound's, because I don't admire his political views.  I do
admire his willingness and courage to be himself, and to take the
consequences.  Revisionist political evaluations of Pound are
inconsequential and darkness-inducing.  The phrase "And I cannot make it
 
cohere" is written at a peak of his powers, not their nadir.
Consequently, it contains ambiguity--the soul of literature.  It can be
read with the stress on "I."  This implies a greater power CAN make it
cohere.  Whatever else he was, Pound was not humble, because he was not
a hypocrite.  He knew his artistic powers.  He was not similarly gifted
in his ability to get on with society at large, of course.  In one of
his earliest  trip to Europe, he assumed the role and manner of a
Spanish nobleman, wearing a cape and feathered hat.  The Spanish
peasants threw cabbages at him, chasing him out of the market square.
Talk about foreshadowing!
6.  As a final thought, why should Pound's "renunciation(s)" of the
Cantos detract from our pleasure in their originality, splendour, and
dependably sporadic brilliance any more than Chaucer's denunciation of
the Canterbury Tales?  He spent a lifetime in the service of poetry, and
provided  this paradiso terrestre with more than "A little light, like a
rushlight, to lead back to splendour." (CVI)
 
You're onto a fascinating topic.   Enjoy!