How to choose between Apple TV 4K 32Gb or 64Gb version?

Yes - I’m using HomeKit. The hub role seems to bounce between the Apple TV and two HomePod minis (setup as a stereo pair), but usually the ATV4K is shown as the “connected” hub (on rare occasions when I check, it seems to be preferred). I’m pretty sure that the HomeKit hub role takes only a few hundred megabytes if that (out of the 32,000 megabytes we’re talking about here :-).

Very difficult to say, the storage is used for app, games, etc. I have gotten by just fine for years with a 32GB version (we have 4 in our house) however if you want the headroom get the 64GB version. Operationally both are identical.

I've got the 32GB version and I consider myself an average user who streams content. The sum total of storage reported used by the 21 installed apps (most not in regular use) is under 1GB. I've got it set to download all the pretty UHD/4K screensaver footage on offer on a daily basis.

The only justification I've heard for the 64GB version is if you or yours are avid gamers with a pair of xbox controllers in regular use. Oh - I've seen another argument in favor of 64GB: "it's only $20 more" (I don't feel this way since it's a pricey box to begin with :-).