You’ve got three fire type moves there which seems a little redundant. Plus, Overheat will reduce your special attack after you use it, causing both it and Flamethrower to become a lot weaker. And I’m not a huge Flare Blitz fan because of the recoil, but that’s just personal preference. Heat Wave is another powerful fire attack to consider.
I would definitely keep Crunch; Arcanine has an awesome physical attack stat and it’s good to have different kinds of moves on your pokemon. Extremespeed is a good, powerful attack that always strikes first. You would have to evolve your Growlithe too early to get it, though (it wouldn’t be able to learn Crunch or Flare Blitz), but I think if you bring a Heart Scale to the move rememberer in Blackthorne City after you evolve it you’ll be able to get it.
I would say have two fire type attacks at most. One physical and one special. And I would recommend that if you do keep Overheat, to make it the only special attack in your moveset because it will reduce your special attack stat after use and you don’t want to weaken a whole bunch of your moves.