All of this assumes the material you are shaping has hardness 8 or lower, so likely stone or wood.
1) Yes. To the wearer of these gloves, the wood or stone door has the consistency of clay and can be affected by hand tools as noted in the description of the gloves.
2) Since you can reshape 1 cubic foot of material in 1 round, it should only take 1 round, but I expect a sufficient strength check would break your lip of wood or plaster or other soft material that you molded over the door edge.
3) 1 cubic foot per round means you can make a nearly 2 foot wide circle about 4" deep. How thick are your floors and walls? I assume it would take two rounds for most wooden construction, and 3-9 for stone. Typical stone walls are 1-3 feet thick while the curtain walls of castles were 7-30 feet thick.