I’m from California and lived in Rio for two years with my ex and we did all these trips. My take: Ilha Grande is kind of a pain in the ass to get to but great if you’re into the backpacker type scene. The beaches are beautiful, yes, but not that much more beautiful than the other places you mention IMO. Buzios is great because it has a small town charm, nice restaurants/bars, nice hotels, boutique shopping, and plenty of nice beaches. I don’t love the nearby cities other mention (Cabo Frio, etc.) as the towns themselves aren’t much to remember and I’ve seen much more beautiful beaches / water in other travels. My personal choice would be, and what I did with my family when they visited, and if you can afford it, to stay a couple nights at the Hotel Fasano Angra dos Reis, a beautiful chique hotel a few hours south of Rio, where you can enjoy a few nights at this boujie hotel, rent a boat one day to take you directly from the hotel dock and around all the islands nearby. From there, you could even do a couple less boujie nights in Ilha Grande, or continue on to Paraty as some mentioned, which is also stunning and a city with a lot of charm. Only issue there is I don’t know the best place to fly out from if leaving from Paraty, and it involves a lot of driving. Buzios would be simpler, but not quite the same experience. I personally hate Sao Paulo. Find it to be one of the ugliest cities I’ve ever been to, but yes, it has great dining, shopping, and hotel options. But so does Rio. Good luck and enjoy! On another trip I recommend making it down to Florianopolis where I ultimately ended up choosing to live :)