We need more information. Doors can mute sound, tame drafts, and create private spaces. Think twice before removing too many of them.

I would keep them. Prop them open for a while, and see if you will still use them. Sometimes very nice to have those doors by stairways.

I would do the eny,mynee, minee moe thing to decide.

depends if you plan to heat and cool the entire home.

Yes, you can remove them.

IN new to you space leave them as mentioned ans seeo how often you want them closed , I do not love doors all over blocking heating and cooling but only you will know what you need .

Some photos would help.

It all depends on if small kids too, and want to keep off the stair steps. I would have given a lot to have doors at top and bottom of steps in the house I lived in at the time, when the grand babies were at the house.

I love being able to close off a stairwell. You can help control heat and sound.