This would either be a major vehicles only update, or spread out across multiple updates
The bigger boat would be nice for the water update and you would have to maybe make it so you could buy vehicles at gas since there are already lifts, and for the bigger heli, you would need to make it hard to get because it would be such a great vehicle
If you wanted to make a more in depth version of the car system model it after rust like this:
You would have 3 different types of modules.
Seating, you would have this be where the driver and passanger sits
Engine, you would need to have one engine to have the vehicle work at minimum, you could make it so you could add a second one of these to make the car go faster
Storage, you would have this be at the back no matter what, then you could have an additional one on the 4 module vehicle base
You would also have different tiers, t1 -t3, vehicles would spawn with t1 modules
T1
Storage- 1 crate
Engine- it works but is kinda slow, slightly faster then walking
Seating, just 2 seats, for driver and passanger
Same amount of health as a wood wall
T2
Storage- 2crates
Engine- this would be about 2.5x faster then walking
Seating- 4 seats, 2 facing backwards, maybe includes 1 crate
Has about as much health as a stone wall
T3
Storage, 6 crates, but takes up 2 spaces
Engine, this would be half the speed of a heli, little less little more
Seatin- 8 seats, maybe 1 or 2 crates
Has as much health as a metal wall
For this you would need to find the t2 in the square/ T2 crates as a rare drop (like circuitry) and t3 in military crate also as a rare drop, but make them blueprint-able for like 500 shreds, so people could make car shops.
Lastly you could make it even further modable with car parts but I don't think that is as needed