You don't really need to buy character sheets. They're available for free online, and you can print them off at home.

It's a good idea to have the three core books (the Player's Handbook, the Dungeon Master's Guide, and the Monster Manual) as well as at least one set of dice per player, including yourself (typically, players bring their own dice, but if you're playing with total newbies you might want to pick some up for them). You will need an adventure to play, but you could choose to either buy one like Curse of Strahd or Wild Beyond the Witchlight, or make up your own in advance. Miniatures and a battlemap are nice to have but not strictly necessary.