RE: Notes
You can take notes on anything involving the game state, but if your opponent asks to see them, you have to show him. Because of this, any notes taken must be written legibly and in plain English (no code words).
I am not sure if there are any restrictions on note-taking though; I look to the others for clarification.
I stand corrected:
Tournament rules:
"Players are allowed to take notes during a game in respect to actions that have happened during the game. Players may take notes during a match and refer to those notes. Players may choose not to share these notes with other players, but a judge may ask to see a player’s notes and request an explanation if needed. A player’s note sheet must be blank at the start of each match."