If the piece is to be free-standing, then generally I don’t need to, but I will if the space is difficult or tight, or if it’s a very large bookcase or a large job.
Most of the time I’m booked up 1 – 2 months ahead of time, so it’s unlikely but you can always ask.
Probably not. Most store bought pieces have been fabricated on a production line so they are not one-off pieces.
Yes, I ask for a 50% deposit to cover materials, which I need before I order anything.