I assumed the VFD was the speed control and the start/stop commands were initiated at the VFD itself not unlike a motor control with start/stop buttons. Remote switching could be an option but not a necessity here. Please steer me in the right direction if I'm going astray.
Both assumptions CAN be correct, but you have to ask your Customer; what is he trying to accomplish and how?
Give you an example. In chemical plants control rooms are often pressurized to keep the flammable chemicals out and allow the room to be non-classiified. There are various openings and doors that are constantly changing the 'leakeage' volume out of the room.
The objective is to maintain a constant pressure difference between the outside and inside, so the ASD controls the volume of air pumped into the room by a pressure differential transmitters 4-20mA signal. Since the drive is in an MCC, remote from the control room a manual start/stop station may be located in the control room and wired to the ASD(Adjustable Speed Drive) itself. There may also be a fire alarm system shutdown wired into it and and alarm signal wired out of it to let people know if there is a problem with the drive.
The ASD's are quite flexible to allow for these various options to be wired in and most of them have integral power supply to power these contacts, although not all and require shielded and twisted pair wires even for the discrete(on/off) signals.
Most manuals are quite good to describe the installation and programming requirements and the factories are helpful. (Early manuals of Japanese drives used to be hilarious with their Jinglish translations.) I am also sure that many folks on this thread would be willing to spend some time on the phone with you if you contact them via a private message, myself included.