I am wondering whether a vehicle has a number of hit points damage boxes equal to 8 + Body/2 (round up). And what tests do vehicle damage modifiers modify. Thanks.

SR4, 158. Yes, they have a condition monitor. Only for Physical damage though, vehicles ignore stun.

Damage modifiers modify any tests that the vehicle is used in (pilot ground for a car) or also attacks with weapons mounted on the vehicle (gunnery).

The short answer is yes.

The long answer is yes, and they have cooler armor.