Congrats on your gig. I would suggest you do a search here, this has been discussed before on here.

There are a million songs you could play. Mostly stay with mid to up-tempo songs. If you play a slow song, maybe it's not to play one that is profoundly sad. Sad theme probably is no problem if it became a staple song. (Some smash hits, even though having a sad lyric, aren't viewed so sad.)

Pretty much play whatever you enjoy, as long as it was a hit song that people will know. And don't limit your setlist to songs from way back when. There are people of all ages in nursing homes, although, yes, most are 70s to 80s.

Mix and mingle with people if you can. Joke with a few of them.

I forgot to ask, do you sing? If so, that will probably go over better.