As regarding rhythm: to compose in sequence of the musical phrase, not in sequence of the metronome.
So I've been thinking about In a Station of the Metro on and off for about 20 years. Recently, I've started composing music and I've revisited the poem because of the ModPo Coursera class I'm taking. I've also been pouring over the Imagist Manifesto. Only now does it dawn on me how to properly read the poem.
Pound is writing in 4/4 time with measures.
The measure breaks are why he had spaces in the original text.
The first THE is a grace note. CROWD, PETALS, and BOUGH are half and whole notes to denote their importance.
I suspect Pound's use of THE rather than TH' was to be inline with his own manifesto and breaking with the metered poetry of old.