For a one person business every ringing phone is a choice between the job you are doing and the job you might get. That is not a scheduling problem you can fix by trying harder.
One missed job a month usually costs more than the smallest plan. If that is not true for you, it is not worth it, and we would rather you work that out now.
No. You can forward the number you already have.
The current plans are on the pricing page, including the smallest one.