Apple provided some data a while ago about what trigger their roaming assessment. IIRC it was something like -70dB - maybe have a search as see if there's an up to date version.
Of one can arrange to have AP's "fire" as perpendicular through walls as possible, it sometimes yields better results. For example, on the party walls on the bedrooms 1/2 and 3/4. Of course, it depends on the antenna pattern also.
How many AP's do you have in hand..?
I’m planning two for the house but that may change. All UAP-AC-Lite. I have one for the garage and driveway as well. Like I said, I’d have to check once we are in the house but my first plan was one for upstairs and one downstairs, but with the solid block walls downstairs it may be better to have both upstairs covering the floor below as well.
With only two AP's it would seem you have little choice but to deploy one in the hall and one on the landing. It could be fine if your use case is fairly low, but there's plenty of structure to get through in such a scenario - not just the walls themselves which may be a bit "wet" if it's new build as the concrete dries out, but also things like water tanks and the possibly any "junk" (vacuum cleaner, ironing board, etc.) that gradually accumulates in the store cupboards (if it's anything like my home.)
Like I said, not adversed to getting another AP if I need it. Might be worth getting an in-wall one instead of ceiling mounted.
It'll be interesting to see how you get on once you move in.
I don’t get handoff issues between my APs. I was just looking to see which APs get most traffic and my ground floor is the busiestby far. Looking at your house layout I would probably install one in the kitchen area, one in the hallway and one on the landing but if you drop your plans into to the UniFi controller software you can map your coverage and see what your optimum setup would be.