I wish you luck. You may be happier taking that $200 to Costco or Sams and grabbing a screaming deal on a LG/Samsung/Sony or other Soundbar with Subwoofer. You will realize better bass response (movies have explosions, car crashes, and others with a nice rumble that neither the $99 nor the full size Homepod can match). You will also have a variety of sound settings for your theater, such as Music, Sci-Fi, Vocal, Cinema, Drama etc. None of these are available as an option with either the Homepod nor the smaller pods. What you get - is what you have.
AppleTV does have a calibration set up for the delay that is inherent in almost any home theater set up, so that is a plus. However, you may find that the AppleTV does not want to stay paired with the Homepods, and you may have to use your iPhone to re-pair them nearly every time you watch a movie.
Siri - well, it's no surprise that Siri is just pathetic. I WANT to like the Homepod product, I WISH I liked the Homepod product, but it falls so far short as a home theater device, that I just cannot recommend them as such. For the price of two, you are better off with an off-brand Soundbar w/woofer.