Sure! Here are my thoughts so far, based on your initial ideas:
Vehicles have armour ratings in addition to weapon ratings.
• Horse or most other mount animals: Armour:1 vs melee
• Bicycle or Motorcycle: no armor
• Sports Car: Armour:1 vs almost everything
• Van, station wagon, large car: Armour:2 vs almost everything
• Armoured car: Armour:3 vs almost everything
• Tank or APC: Armour:4 vs everything
Vehicle Aspects: Being in a vehicle or mounted is an automatic, free Aspect which can be tagged once for free. Subsequent tags cost a Fate Point. Players can use Declarations to add additional Aspects or a Gun to a vehicle.
Zones: Vehicles, by default, have one zone, and a Zone Border equal to the Armour rating. Except for horses, you cannot directly target an occupant within that Zone unless you are either in the same Zone, or overcome the Armour rating with your Weapons or Guns roll. Large vehicles, such as boats and cargo vessels, can have multiple Zones, and depending on circumstances, you cannot cross from one Zone to another without overcoming the Zone Border, unless there is a specific Aspect you can tag to allow easy access.
Weapons: personnel on a vehicle use their own Weapons or Guns; vehicles with an on-board Gun allow a user to use their own Weapons score. Effective ranged combat requires cooperation between the driver and any passengers, so everyone's Guns skill is Modified by the Driver's Driving Skill (good drivers are effective at setting up shots for their gunners, while bad drivers jerk and change course at inconvenient times).
Movement: A driver can move one zone with no action or sprint (using Driving, Athletics or Survival) with a supplemental action.
Defense: Driving should be usable as a defense when in a car, and Athletics or Survival when on a horse.
Other Skill Checks: Passengers using a Skill check in a moving vehicle are not considered to be taking a supplemental action, and are not penalized for the movement, except for a rider on a horse or other animal. That said, almost any Skill roll which involves hand-eye coordination will be Restricted by the driver's Driving skill (especially if the Driver is trying to attack while driving). Certain skills may be Modified instead by the driver's Driving skill, getting a +1 or -1 based on relative ability: Guns, when used to attack passengers in or on another vehicle, benefits from a savvy driver's coordination, but likewise suffers from a poor driver's untutored driving.
Vehicle Skills: Vehicles can have stats just like a character does.
• Maneuverability: A vehicle’s Maneuverability reflects its speed and handling. It Modifies a driver’s Driving skill. For attacks on the vehicle, it works in reverse: the vehicle’s Maneuverability is Modified by the Driving skill of the driver. Otherwise this is like the Athletics skill. 4 is suitable for a motorcycle or sports car, 3 is for a regular car or truck, 2 is for a van, lorry, or light cargo vehicle, while 1 and lower are for a heavy cargo vehicle, armored tank, or construction vehicle.
• Endurance: A vehicle’s Endurance determines its Stress track, and its resistance to Hexing or other attempts to disable the vehicle. 1 is suitable for a Motorcycle, 2 is for a sports car, 3 is for a regular car, van or truck, 4 and higher are for armoured cars, cargo vehicles, construction vehicles, lorries, etc.
• Might: a vehicle’s Might determines its ability to carry or tow personnel and cargo. Figure the carrying capacity as 20 times the equivalent Might of a human. 1 is suitable for a Motorcycle, 2 is for a sports car, 3 is for a regular car, 4 and higher are for cargo vehicles, trucks, etc.
Mounted Animal Skills: When you don’t want to provide full stats for a mount creature, you should still determine the following skills.
• Maneuverability: A mount’s Maneuverability is functionally the same as its Athletics skill. For attacks on the mount, it works in reverse: the animal’s Maneuverability is Modified by the Driving skill of the rider.
• Endurance: A mount animal’s Endurance determines its Stress track, and works just like any other creature’s Endurance.
• Might: A mount animal’s Might determines its ability to carry or tow personnel and cargo. Horses usually have Inhuman Strength, while other Mounts may have Supernatural or even Mythic Strength.
Weapons:
Animal Mounts: Trained warhorses or other combat-ready mounts have the equivalent of the Claws power (Weapon:2), usually enhanced by Inhuman or greater Strength.
Ramming a Pedestrian: A vehicle in motion used to ram a pedestrian acts as Weapon:5 by default (except motorcycles, which are Weapon:2), and use the driver’s Driving skill to determine a successful attack. The driver can sacrifice 2 shifts to affect every pedestrian in a Zone, or split up the attack as a Spray attack to be more precise about which opponents are struck. Common sense should determine how precise such an attack should truly be. Parked vehicles which are used to strike a pedestrian are just a Weapon:2, and use the driver’s Driving skill to determine a successful attack.
Optional: for added variety, use a vehicle’s Might and Maneuverability skills to Modify, Restrict or Enhance the Driving skill depending on whether or not you rule speed and mass to be a benefit or liability.
Ramming Another Vehicle: Against other vehicles, a vehicle’s Armour rating determines its Weapon value (minimum Weapon:1), unless it has been weaponized with additional Aspects, such as Spikes. Direct vehicle-to-vehicle ramming attacks are resolved by a contested roll between the Driving skill of the two drivers, Modified by each vehicle’s Maneuverability. Successful attacks deal Weapon:X damage against the Vehicle, reduced by its Armour rating.
Mounted Weapons: Additional Weapons mounted to a vehicle can be Declared with Resources, Contacts or other appropriate Skills checks. Mounted Weapons can range from Weapon:1 for minor inconveniencing effects like Dart Guns or Spikes, to military-level Weapons as high as 3, 4 or even 5. “Melee” Vehicle Weapons like Spikes use the Driving skill of the driver, modified by the vehicle’s Maneuverability. Ranged Vehicle Weapons like Machine Guns, Rocket Launchers, Grappling Hooks and similar Weapons use the Guns skill of the gunner, Modified by the Driving skill of the driver.
