I am installing 3/4 X 3 1/4 Brazilian Cherry in a hallway with 5 doorways and a landing at the top of a short stairway.

I'd appreciate your opinion on how I plan to handle the transitions at the doorways.

1. Four of the doorways are bedrooms, which will remain carpeted. The existing carpet for now, but will eventually re-carpeted. Two doors are parallel to the new floorboards, and two are perpendicular. My plan is to simply end the flooring beneath the center of the door, by ripping a floorboard to size (hopefully nearly a full board) at each of the parallel doors, and on the perpendicular doors, install a board crossways under the door. (I'll just plane off the tongue) Then, tack the carpet up tight against the new board.

2. One doorway, a bathroom, has a marble threshold. I plan to undercut it slightly, and try to fit the new boards (they'll be perpendicular) either just up to it or slightly under it, and caulk the joint. I would expect the need for expansion to be the least along the end grain, so minimal spacing.

3. On the stair landing, I am butting perpendicular to a piece of nosing. Depending on the layout, I will need to spline either the doorways, or the landing.

sounds like a good plan. one thing is that where the carpet meets the wood i usually end the flooring center of the door slab when its closed. usually thats not in the center of the casing but about a 1/2" behind the stop. this way you see wood from the hall when the door is shut and carpet from the bedroom when the door is shut.

Exactly. On the parallel doors, which are on opposite ends, an even number of boards fall pretty close to the center. Since my plan is to plane the tongues off of the final boards, I can certainly reduce the width on one or both, to make it fall right in the middle. On the perpendicular doors, you will see part of the cross piece from the floor side, but I think that is OK.

I'm a bit concerned about height matches between the two floors. It seems that most carpet and pads will be about 3/4 (or less) thick, which should make for a good transition. Also, I am wondering about potential wear from foot traffic on the sharp edge of the final board where it meets the carpet. (probably not a big concern)