If you buy from a reputable builder, all these and more can be built into your property. Just make sure you arrange it all,
confirmed in writing, before you sign the contract.
Many properties, mine included, did not have a hand rail up the stairs, because despite my attention to detail, it simply did not occur to me that there wouldn't be one .... there is now
You might also consider the width of doors for wheelchair access.
Disabled or not, you might consider that the open plan style of most properties makes heating and cooling difficult and expensive. Walls and doors, especially to isolate the staircase, will make the property much easier to keep warm at this time of year, so brick up those arches. Separate rooms are good