Chaos magician don't really need a mentor spirit, but if it does, I would see something less mythical and more "modern" than Salamander.
Salamander seems to me more adapted to classic hermetic mages, studiying alchemy, searching for the philosophal stone, and so… you get the picture.
For a Chaos magician, I'll choose something linked to the modern life, "Trader", "Power", "Luxury", "Fashion", somethin' like that, and search in the mentor archetypes which one fits the best.
About your Salamander, I'd say manipulation spells ; but I don't like the daylight disadvantages as it is designed, not because it's unbalanced, but because I think it won't be fun to play, for the player and for the GM. I prefer let him engage in social activities, but give him a stronger malus (-2 to all social tests), and describe the character's attitude : moody, half asleep, shy and so.