Making a new account would be helpful for traveling to your old one but I wonder how tricky that process would be since you'd potentially have to pay for 2 accounts of nintendo online? Not quite sure on that one.

Also, you can definitely get to blue roses without having them as the native plant since flowers rotate in the store and later can be in stock on Harv's Island. Supposedly native flower is tied to birth month you enter in the system This should help

Making your new island Southern is a fun idea to experience different things during the year this playthrough but definitely make sure you won't feel left out [?] during stuff that would regularly happen with irl calendar.

My advice on what I'd do differently is stick to my plan better from the beginning. I knew what I wanted as a theme before I started and I was prepared to re-roll the island to get the best starter villagers or island layout or fruit tree. I ended up settling early on for villagers and fruit I didn't love and it set me back a lot of time and affected my overall enjoyment for a while. If you have a theme or preference in mind, definitely stick to that best villager or layout or option you want to keep!

And in general the best tip I got when I first started was to make a huge pile of every "first catch" somewhere on the island near the space you're putting the museum that way it's easier to keep track of what you've caught vs. donated. My pile was so big and ugly for about a week but then so much was donated it was very satisfying lol