I used to DJ swing dances back in my dancer days. One thing live bands get wrong when playing for dancers is playing music that’s hard to dance to. Nothing kills the vibe of the room like playing a song that’s not danceable after a couple songs that have filled up the dance floor. When you play more modern music, the definition of “danceable“ becomes a little more liberal, but it’s still a thing. Of course, at a wedding, this might be OK. Gives people an excuse to get off the floor and rest a little bit or socialize.
But when preparing a DJ set, I would actually plan my set out for the full-time length that I needed. I would alternate songs by tempo and dance style: a rockabilly number followed by a downtempo Lindy Hop followed by a Charleston or Balboa number and then maybe a blues shuffle or slow dance. But then I always had other things “in my pocket“. I had whole playlists of fast Lindy songs, downtempo Lindy songs, rockabilly numbers, blues songs, etc., so I could “read the room“ and play more of what the audience was responding to. I would plan some very good sets, but the room was different every time, so this method saved me from laying an egg on the stand. It also gave me something to fall back on if I got distracted or was still hunting for a song that I wanted to play when something was ending…I had something always in queue that I could throw on while I got ready.
I imagine planning a band set could be the same kind of thing. Have a planned set list and then have extras of each type of song that you can play more of if the audience responds better to that. Of course, at a wedding, you may already have guard rails regarding genre, tempo or song style.