Gearbox.. most important because if there's no warranty it'll cost you a fair amount even for just a repaired/reconditioned unit. Try to get someone experienced* to help you with this as describing the symptoms of a worn-out or bad gearbox won't really help you identify it easily as it's mostly from feeling and/or hearing. The second would be the turbo unit and its oil feed lines as some owners do not spend much on their car maintenance, and most like to drag, so if it's full of sludge, you may want to check that it still can be brought back to good health by servicing.

Some others include engine/transmission mounts which normally spoil quickly, and suspension depending on how the previous owner drove it and/or how much load they normally carry. The ones that like to fly over bumps and drive fast over rough roads will probably have caused their suspension to wear out quickly (especially the rear section).

Try to bring someone who's familiar with the Preve/Suprima to help you. If not, try to arrange to bring the car to a reputable workshop familiar with the Preve/Suprima and get them to do a thorough checking for you.
*Experienced as in familiar with the Punch CVT gearbox and its characteristics and how it feels like when it's not healthy, not someone who is familiar with other cars with Auto Gearboxes and etc.