The whole Resident Representative gimmick is just an evolution from the Mayor gimmick in New Leaf. My other half had New Leaf and was mayor in the town we shared, so she got to decide everything unless I went on as her. The crafting etc is something that I think has been brought over from Pocket Camp, and fortunately for us isn't hidden behind a Paywall. Other than that it's the same Animal Crossing experience as usual. The first week or so has felt a bit grindy with things being drip fed to me, but now that I have the Resident Service building instead of the tent it feels a lot more like the usual Animal Crossing experience. I like the crafting elements. The durability of tools can be a pain in the arse when you need to craft 4 axes while you're doing your daily woodcutting, but it's keeping me plenty occupied. Nintendo have said the one island per switch limitation is because of how the game is saved. I think it was similar on the Wii version.
The code thing for people visiting your island is for if you want to invite people over who aren't on your friends list. So you can open the gate and allow three different sets of people in, either anybody on your Switch friends list, anybody you've added as a "best friend" in Animal Crossing, or anybody with the Dodo code which is generated every trip.
If you came over as just a friend or through a dodo code you'd be able to use my shop, fish, craft, talk to my islanders and catch bugs
If somebody is a best friend I think it means you and they can also dig things up, move things around etc on your respective islands. You can also fire texts and gifts at them in the game. This morning I visited a best friend's island and started to organise their trees and flowers ahead of the "project K" part of the day. We've also been sending random furniture and clothing at each other.
I think I'm still a little ways behind some people, but that's probably because it was evening on launch day when I started playing, so I lost a couple of hours.
It's actually making me want to dig out my copy of Let's Go To The City and give that a play, as for some reason I never played that much. I think we went on a holiday and we're scared to go back on.likewise our copy of New Leaf hasn't been touched in years. We're both scared our favourites would have moved away.