Hi @wcpeixoto, welcome to the Sonos Community!
Thanks for sharing the floor plan image: it’s helpful to see the full picture before recommending anything. To answer your questions:
“Whether the Sub Mini might be a better fit than a new full-size Sub”:
I would say stick with your Sub Gen 1. Instead of buying a Sub Mini, you can just use your Sub Gen 1 as it’s compatible with the Sonos Arc or Sonos Arc Ultra if you decide to go that route and still works with your current system. The only reason I would suggest upgrading to a new Sub would be if you want to use dual-subs.
“If Arc or Arc Ultra would be overkill for this space”:
The Arc or Arc Ultra would bring the cinematic feel that you’re looking for without going overboard. You’ll get clearer mids and highs with the Arc, as well as the option for spatial audio with the up-firing speakers, something you won't get with the Beam. However, if you are able to, I would suggest waiting until you move before looking at replacing the Beam with the Arc
“Best use of my existing Play:1s or Ones for surrounds”:
As a quick note, if you decided to go with the Arc Ultra, you won't be able to use your Play:1s as surrounds, but you can use your Sonos Ones. Otherwise, I would use two of your Sonos Ones as surrounds and the rest of your Ones and Play:1s placed throughout the condo, i.e. one or two in each bedroom, then the rest around the dining room and kitchen.
“Placement tips for a clean and optimal setup”:
As you can move your Sonos Ones and Play:1s later I wouldn’t worry about placement too much: however, we do have a support article for selecting a speaker location. I would recommend placing them and playing something to the whole system, then walk around and listen for dead zones where you could put a speaker or move them closer together. Otherwise, make sure to follow our surround sound guidelines.
If you’d like more details on our products, then our sales team are here to answer any queries you may have. You can contact them and send over your floor plan where they can give their suggestions, as well as help you set up an order if needed.
I hope this information helps!
There’s no-one getting any sleep in either bedroom that backs on to where the home theatre speakers will be! 

Nice crib.