Here are a few answers for you:
The workroom is a career room as well as a place to work on a hobby.
Some careers use the workroom exclusively (i.e. Dress Maker, Denture Maker, Watch Fixer, etc) Any career that doesn't 'fit' for the kitchen or the office uses the workroom.
Picking up one item: That's the way the game was designed.
Certain items can be returned to the store prior to use. To do so, click and drag (or tap then 'drag') the item from the tool tray back to the store. Almost all items are one-use only (praising/scolding hands do not apply here).
The floor repair kit only fixes 1 hole. In order to fix the other holes, you must purchase more floor repair kits.
Hope this information helps.