hiiii!
hell yeah anon!!! first time in brazil for an INCREDIBLE reason!!! i'll be going to RiR with my friend myo hehe cannot wait to see each other in person properly this time around instead of jumping from different sections at a concert kdjfhsdfksd

ANYWAY!! you actually asked the "right" person for this bc i work with tourism skjfdhsdkf i also love talking about trips, so double win!! since idk what things you like , i'll give very general recommendations:
- if you do not speak portuguese at all or some spanish, my rec is to stay in the south zone (Ipanema, Copacabana, Leme, Leblon). it is the more touristic area which means it's more likely that you'll encounter services offered in english and things like that! it is also considered the safest neighborhoods in Rio. this means that it is also a bit pricier to stay there than elsewhere, BUT imo it is worth it,especially if it is your first time in brazil
- if you want to go see christ the redeemer, pls know that it'll always be crowded sjkfdhsdfs my rec would be to go as early as possible (i think the first train from the visitor's center to the base of the stairs is 08:30, but i might be wrong, i would have to look it up), it is possible to get a better view of the surroundings. last time i went, i hiked up BUT do not do this on your own :D i put myself and my friend in somewhat of a risk bc i like walking and that was a bit dumb. it is just forest and mountain and it is very isolated, there is like no one there. just... don't do that on your own skjfsdhjf if you want to hike the corcovado mountain, there are tours/guides for it!!
- you SHOULD (if you are active and enjoy these things) hike the Urca Mountain, which is the sugar loaf. then you can take the cable car down!! it is a beautiful hike overviewing the ocean!! but you can go up and down through the cable car. it's fun!! ah. EVERYONE wants to go up there to see the sunset (understandably), if you don't like crowds, go a bit earlier!!
- copacabana and ipanema beaches are must!! there are a lot of things to do as well (surfing classes, beach volleyball, altinha, beach tennis, etc.), you don't have to partake in any of it, but you can. just ask if it is paid first bc some of them are like, acutal lessons ksjdfhsd
- you should DEFINITELY see the sunset at arpoador!! gorgeous. it will be crowded sjkfdhdsf sorry i keep saying that, but it is one thing that i personally like to know before hand!! but it is totally worth it, gorgeous views.
- now, this one is a bit "harder" to do just bc you have to check the tide first. but joatinga beach!! it is inside of a gated community, the problem is that it is tiny, so there are a lot of times in the day where you cannot go to the beach bc you are stuck on rocks since the tide is high.
- not sure how long you have but!! totally worth doing a downtown rio excursion. there is a loooooot of history and beautiful architecture to look at!! it is more inland, so it shows you a different side of the city!
- santa teresa is a bohemian/historic neighborhood, very different from the rest!! would recommend as well!!
- hmmmm idk if you like football skdjfhhsdfs but if you do, going to visit the maracanã stadium is WORTH IT!!! there is a vibe, idk how to describe it.
- hmmm there are the botanical garden and the page park (gorgeous), worth every second in there in my opinion
- when i went last time, i stayed in a completely different neighborhood (where my friend lives) so i'll have to owe you restaurant recs, im sorry!!!
- but these are just like, the most popular things to do, since idk what kinds of things you like, it's a bit harder to give specific recommendations hehe

BUT!!! i hope it helps a bit!! and i hope you have the best time in brazil!!!