2) The wood flooring is going to have a finished level about 20mm above the carpet. That rules out just using a z-strip gripper, since they seem to have a maximum height of 14mm, and implies a moulding to get the height of the wood down. The door opens onto the carpet.
I'm thinking about something like this: W = Wood, T = Threshold, C = Carpet, G = Carpet Gripper, D = Door, Z=Z-strip,S=Shim. So the carpet is held using a grip strip, rather than an edging bar, and then the threshold covers over the nail points. I expect the thickness of the door to be less than the total width of the threshold, so I will arrange it so that the door is aligned with the carpet side of the threshold.
DDDDDDD TTTTTTT WWWWW TTTTTT WWWWW TTTTTTTTTT WWWWW TTTTTTCCCCCCCCCCCC GGG I can construct that reasonably easily using a couple of mouldings I've already got.
Alternatively, I could modify a reducing moulding I've already got to get the height down a bit, attach it to the main wood floor by routing a tongue on, and then use a z-strip ... Disadvantage there seems to be that I end up with a little groove that will be hard to clean, and I have some metal showing on the wood floor side of the strip.
DDDDDDDD WWWWW ZZZZZZZZZZ WWWWWWWWW Z ZZZ WWWWWWWWW ZCCCCCCCCCCCC
Third option is making something like an Easy Shim (S), so the carpet height ramps up. ZZZZZZ WWWWWWW ZZZZZ WWWWWWW ZZ CCCCCCCCCC WWWWWWW SSSSSSSSSSSSSSSssssssssss............
Any thoughts/standard solutions?