Meanwhile some further info that perhaps may assist you…
Note: you cannot setup a brand new S1 Household with a product that is both S1/S2 compatible, so you cannot do that with your Ones, Three, or your Playbase products - so you must use one of the Play:5 (Gen-1’s) in order to create that type of system. You may want to consider that option at some point.
Any devices that are both S1/S2 compatible (except for Sonos One-SL speakers) that have been upgraded to S2, once factory reset, can still be downgraded to S1, using the downgrade tool that’s available in the S2 App only - see this link:
https://support.sonos.com/s/article/5097
So note, a One-SL speaker cannot be downgrade to an S1 HH but you are fine to do that with Sonos Ones, Three and Playbase
It’s advisable to remove the S2 App when setting up an S1 Sonos Household after downgrading the compatible products.
The above information is just in case you prefer to run ALL on one single S1 Sonos system, perhaps consider that option a little later, when you have everything up and running.