The DC supply (Vcc or Vss) to the [a] should be less than the maximum collector to voltage for the transistor you intend to use [c] will also depend on the available power supply.
Not without fall. Exist the electronic schemes, in which is used serial cut-in transistor. Also, there is schemes, using avalanche mode.
If it is limited current of the transistor, that voltage of the power supply can be more limiting voltage of the transistor. But worker voltage (not supplying voltage) must not exceed limiting voltage of the transistor.
