As in, you design and choose where to put this and that button, the angle of the dashboard and so on? How do you deal with function vs form?
Buttons - yes, but at a later date.
Right now its:
Position and location of the occupants. Size and location of the wheels and tyres. Location of the powerpack (engine, transmission, e-motor etc). Location of the filler pipe, charge port, pedals, gear shifter, etc. Overall height, width, length of the vehicle, wheelbase, track width, location of the 100's of modules in a modern vehicle, wiring routings, Occupant vision. Meeting legal dimensions... It's a rather long list.
Function Vs. Form.
Primary principal - it's designed around the customer (and for a van what the customer wants to put into the cargo area).
There are inviolables that the felt-tip fairies MUST respect (Vision, cooling radiator pack height, ingress / egress, ergonomics,
The rest is negotiations with the design studio - sometimes emotional, occasionally rational...