the whole concept of a viceregal cavalcade seems pretty foreign to modern eyes, and poorly documented by contemporaries, so we mostly have to try to reconstruct it based on Joyce's clues.
the viceroy represented the British king, and had only been in that position for a couple of years, the eighth viceroy since the Phoenix Park murders.
cavalcades were occasional big productions with lots of horsemen in fancy outfits, which average Dubliners enjoyed as a spectacle unless their politics intervened. the female observers were most interested to see the women's dresses. ("pearl grey and eau de Nil")
the newspapers would have announced the approximate time and route, so you'd expect pedestrians to gather, but we don't hear about any. (p174: "Hello, placard. Mirus bazaar. His excellency the lord lieutenant.")
everyone was encouraged to greet the viceroy and these greetings were returned as far as possible. (cf the fine old custom about funerals in episode 6)
traffic was apparently supposed to stop to show respect?
p238: "Clatter of horsehoofs sounded from the air. --What's that? Martin Cunningham said. All turned where they stood. John Wyse Nolan came down again. From the cool shadow of the doorway he saw the horses pass Parliament street, harness and glossy pasterns in sunlight shimmering. Gaily they went past before his cool unfriendly eyes, not quickly. In saddles of the leaders, leaping leaders, rode outriders. --What was it? Martin Cunningham asked, as they went on up the staircase. --The lord lieutenant general and general governor of Ireland, John Wyse Nolan answered from the stairfoot."
"William Humble, earl of Dudley, and Lady Dudley, accompanied by lieutenantcolonel Hesseltine, drove out after luncheon from the viceregal lodge. In the following carriage were the honourable Mrs Paget, Miss de Courcy and the honourable Gerald Ward, A.D.C. in attendance." (so just two carriages?)
"sunshades spanned and wheelspokes spinning"
"the leaders' skyblue frontlets and high action" [are leaders and outriders different?]
"glossy horses pranced"
"gent with the topper" "fellow in the tall silk"
"with his following"