Should I use a fast & charge TM on my Houndoom?

Yes. Personally I like Houndoom for Dark type moves and the other dog, Arcanine, for fire type moves.
I live in an area where both are really common and have had to TM them myself as well. Never once got a Double Dark Houndoom through evolution.

I would wait. You might catch Tyranitar with iron tail/crunch next week. No need to TM or power up for something that hasn't been released.