I have the maximum 8 player characters since my island is based around world history and the cultures that have existed, do exist, and hypothetically will in the future (so I could justify having a robot villager lol), so I wanted to include as many different representatives as possible.
So, typically at bare minimum (though sometimes I make exceptions if I just can't be bothered to do it), I'll load them all up individually each day I play so they can all get the daily points from the kiosk. This might be the limit of what most of them will do in a given day, it depends on the day. I'll also talk a little bit with the animal residents, partly because I do like them and partly so they don't waste time with the "Where have you been? Have you been ignoring me?" dialogue.
I check out what's in stock at the Nook's Cranny and the Able Sisters' shop and, if there's furniture/wallpaper/flooring that I think would fit a particular character, or clothing that I want for that character's wardrobe, then they'll get to go shopping for said items as well. If there's nothing notable, I don't bother with this.
Either my main character or one other particular character will go around my dedicated farming section, collect the fully-grown produce, and water everything.
One of my characters is supposed to be a professor, so since my main character already has all of the ranks, I let this professor character collect all of the daily fossils and get them analyzed so she can get the achievement ranks and associated titles as well.
I'll check out Kapp'n's mystery island each day with at least my main character, the Resident Representative, though I might also do it with a couple other characters if it's a particularly good island, or if I want more gyroid pieces, if I have the time to do so.
Frequently, but not always, I'll head to Harv's island so I get at least my main character's fortune told since I want the items she sends you if you have a bad luck day. Whether I bother with this with other characters depends on the day, how much time I have to play, etc. If it's a new week, I'll see what Redd, Kicks, and Saharah have in stock.
From there, it depends what's going on that day. If there's a special visitor like Gulliver and Gullivarr, sometimes Redd (depending on his stock), and sometimes Wisp (I don't bother with it as much as in the early days of the game), I'll engage with them. Always do Gulliver and Gullivarr's missions with everyone each time for the items and eventual Golden Shovel DIY.
I don't really bother with K.K.'s shows most weeks, but sometimes I'll indulge. Usually only with one character, but maybe more if I feel like it.
If there's nothing else going on (if it's a special visitor that's not Gulliver or Gullivar) and nothing much to do on the island, I'll head to Happy Home Paradise and do some designing there. I only do this with a few of the characters in particular though.
Since I have 8 characters, I like to give them each their own days to get the focus as opposed to the rest. Just depends which one I feel drawn to on a particular day.
I don't play every real life day, though. I often take breaks and concentrate on other things in life, and other games. I'm currently in such a break period, haven't played in a few months. Will revisit it sooner or later though.