I think as far as the repeat villager pattern:
You do have to keep in mind that the more islands you go to, the more different villagers you see, and therefore there is a higher chance that you see one you've already seen on your next island due to the pool of villagers you haven't seen becoming smaller with each new one you see.
It's very similar to the Birthday Paradox in that the odds of 2 people in a room having the same birthday are about 50% when there's just 23 people in the room. As you add each person going up from 1 person in the room, the pool of birthdays that no one has yet gets smaller and smaller each time, and it reaches 50% quickly, at 23 people. There are 366 possible birthdays, so I assume that the odds of seeing a repeat villager (given there are about 400 different ones in this game) reach 50% at around 30ish, maybe even more like 25-27
here's an article on the Birthday Paradox:
https://betterexplained.com/articles/understanding-the-birthday-paradox/