2. Old salts are old sailors and fishermen (from salt water), a sailor's home is a retirement home for old sailors. Cherry stones are the pits in cherries. Making small, intricate carvings (usually in whalebone) called scrimshaw was once a favorite pastime of sailors. I imagine that retired sailors might make carvings of heads from cherry stones (pits) but I don't know what they look like.
3. The building has at least two apartments per floor, some facing the street (front) and some facing the rear (back). Dulcie's room was on the third floor at the back (rear) of the building.
4. Pinkle Worksis the name of a company that sponsored (issued) the calendar with their name on it, then gave them away free as advertising.