Any console, any game. Everyone runs the game on their own device, in lockstep — only controller input crosses the network, so your own buttons are as immediate as they are offline.
Read the code out, or send the link — the link already knows the console and the game.
Pressing Start opens the emulator and the room. Nobody's game begins until every player's console has finished loading — that is the start barrier, and it is what makes frame 0 the same moment for everybody.
Five characters. There is no I, O, 0 or 1 in a code. Pick the same console — the game is whichever one the host is on, and your console follows the room rather than your pick.