A few years ago I built the Google AIY Voicekit, I just barely managed to get it working because I'm very poor at the software, and when it stopped working after a month or two, I moved on to other things, and it's been sitting in my basement. But yesterday I succeeded, to my amazement, in installing Homebridge onto the Raspberry Pi in the device. I then even got it installed, as an accessory, in iOS' Home. (Although I haven't figured out the next step there, or with Google Home, either. I don't really get how to install plug-ins yet.)
I have ordered a Hubitat Elevation, which should arrive in two days. Will the Hubitat help me / be useful / make redundant the Homebridge I've just now got running? How much "overlap" will there be? I'm afraid of biting off more than I can chew! I have iOS Home running on an Apple TV, and a few devices, but mostly I use Google Home to talk to / query my lights, Nest thermostat, and Wyze sensors.
And -- is it possible for Homebridge, or Hubitat, to utilize the speaker in the Google AIY Voicekit to, e.g., announce notifications? I think this is "just" a software thing, in that the Raspberry Pi in the AIY Voicekit has a speaker in/on it and should be able, theoretically, to be made to speak, as it did when running its previous software.
As you move into the Hubitat Universe you'll find that Raspberry Pi will be quite handy. First, Hubitat has community built connectors to Homebridge. You activate/enable/install a built-in App called MakerAPI and add the matching Homebridge Plug-in on your rPi. Then, devices you select on Hubitat will show in Apple's Home App.
Your Raspberry Pi (rPi) can also run Node-Red, which is a tool for visualizing automations. It also uses a MakerAPI instance to send device actions (events) to and from Hubitat.
For voice announcements, Hubitat has a Google Chromecast driver, and so does Node-Red.
I must admit to not knowing anything about "Google AIY Voicekit" BUT I am using a Google Home Mini as my announcement device with MP3 sounds and TTS. The majority are via Node-Red now, but all of it began with the Hubitat Chromecast driver.
There's a great topic on Node-Red Samples that should help with ideas on how to join it all together.