Alright, here are some considerations that should be made. First, lets look at what this described biology actually looks like.
With your given body plan, there are two ways they could fold up their wings (yes, this is important). They could use the standard tri-fold pattern that birds use, which would result in them carrying their hands at their shoulders while 'resting.' Alternately, they could use a more human-like method and let their arms hang at their sides so that their 'hands' hang low, and fold the other half of their wings up alongside them. Whatever way they handle this...their arms are going to be long. Assuming an average humanoid shoulder width of 1.5 feet, this means that each wing averages about 11.75 feet long...meaning that the 'hand' on the wing can be fully extended from the body to a length of about 5'10", which is actually a longer reach than they are tall. Given this, they are more likely to carry their arms tucked up so that they can wrap the 'fingers' of their wings around themselves so they aren't dragging anything on the ground.
To give a quick explanation of why that was important...it is to show that using their arms will be very, very unwieldy in enclosed spaces. The distance between their elbow and wrist is, on average, 2'11"...which is a full 10" longer than the average length of a human's entire arm. Their 'arms' aren't going to be very useful for every day tasks.
So, now that we have that established...let's look at architecture.
The first thing I'd note is spaciousness. An average human needs around a 6' square space to fully extend their arms and stretch out. One of your flying humanoids needs a 25' space to properly stretch out. Birds are happy in tighter spaces because they don't just "hang out" at home and aren't too concerned about being able to spread out and be comfortable while at home. Assuming your avian-folk like to stretch out, I would expect their homes to have an extremely open floor plan intended to allow them space to move around. An ideal design would be to have enough space within their homes to be able to fly...but that would require an extremely large house, and would likely be limited to the wealthy.
I imagine that they would have some spaces that were tighter, for economical reasons, but I imagine every one of them would seek to have at least one room where they could actually stretch.
The second thing to note is that for exterior floor changes, stairs are unnecessary. You may have stairs inside of a building that is all a single unit (like a multi-floor house), but a multi-level apartment building would have no need for stairs as long as there was a large enough open space at each level for them to land on. In fact, outdoors (where space isn't a big deal and they can freely spread their wings) or in very large buildings, I'd imagine that elevation changes were simply handled by flight, rather than by stairs or ramps (with some allocation perhaps provided for those who cannot fly themselves due to injury or disability). Additionally, since it allows you to start off at a greater altitude, multi-floor buildings would be likely to have their entrances located off the ground level. Not only is this convenient if you are flying in (you don't have to go down as far to get in), but it is also great for keeping out a lot of pests that might otherwise enter through your doors. Perhaps even single-floor buildings would have their entrance on the roof, rather than at ground level.
As for interior design considerations...as was mentioned, their arms are unwieldy for most tasks and, as you mentioned, they have chimp-like feet. However, the construction of the 'hands' on their wings are likely to be better suited to delicate and precise work than the 'hands' that are their feet. As a result, we would probably see a split in design layouts based around this: The feet are used for grunt work and simple tasks like lifting, carrying, moving, fighting etc. and the hands are used for precision work such as sciences, crafting, and other things requiring finer dexterity than what their feet could offer. As a result: storage-type furniture would probably be located close to the ground, as would handle and grips for opening said cabinets, so that they can easily use their feet for managing these. But, storage for lighter, more precise things like tools could be positioned higher up where the arms and hands could easily get at them.
Workspaces would probably see a similar divide...you'd have some things positioned low to the ground for tasks that used their feet, and some things positioned at what we'd consider a more normal height (with plenty of space around them) for use with their hands. Tasks like kneading dough would be best handled by their feet as it makes use of the sturdier nature of their feet...and avoids getting dough in their feathers (another important consideration for them).
Given this division, we would also be more likely to see 'sinks' situated low to the ground where they could wash their feet more often to do clean work, like food prep that required more force.
Bathing areas would have to be expansive...to properly clean their wings, birds have to spread them out entirely and work over the entire wing. Baths would likely be more common for them than something like a shower as it is simply easier to manage cleaning feathers on standing water than it is by spraying water on the feathers (which are generally somewhat water resistant). Poorer people may only have baths large enough to wash one wing at a time, and even then may have to scrunch up a bit to fit...either way, their bathing spaces would be bigger than ours.
Given their tail feathers, as you mentioned, seating would have to be redesigned as well. There are two different ways you could handle this...
1: Their seating could be in the forms of cushions situated on the floor that they knelt on, much like how a bird 'sits.' This would bring any 'sitting' workstations down nearer the ground (more in line with the 'foot' spaces they would have).
2: A seat more like a traditional massage chair, but without the head rest. This allows them to sit down with their tail feathers hanging off the back of the chair, rest against the chest rest, and either set their feet normally on the ground, or tuck them up onto padded rests like that image has. This would keep their arm workspaces up off the ground, and also potentially allow them to sit at what would otherwise be a standing workspace.
I'll probably think of more of these later...but there's a good start for you.
