Chat for a large number of players

I'm whiling to use a lobby chat in my game. It's a chat running in the first and main server. ALL the players who are running the game and are not playing in a private game are able to chat. Alright, here comes the problems:

It's possible that will be over 500 players online in the lobby connected to the chat server. Aren't 500 players too much to stay connected together to the same server?

The only way to create a chat system I've ever used was using RPC's. RPC's will be alright to 500 clients?

Are there other methods I can use to create a chat designed for hundred of players?