(a) I love that body. Didn’t use it myself, but I love it. (And yeah, the headlights are a bit dopey, but that’s cute. 
)
(b) Remember pit stops are at percentages - if you’re having two, they should probably be at 33 and 67, 35 and 65, 40 and 60 … something like that. The defaults are set up for a 4 pit stop race.
© Reposting my formula for estimating fuel consumption:
Estimated Race Fuel Consumption [in kg] =
(Time of Race [in hr])
* (Engine Economy @ Max Power RPMs [in g/kWh])
* (Engine Power @ Max Power RPMs [in kW])
* 1 kg/1000 g
* r
…with r likely in the range 0.44 < r < 0.61 for low-fuel-consumption tracks like the Automation Test Track (point estimate 0.52) and 0.53 < r < 0.75 for high-fuel-consumption tracks like Norisring (point estimate 0.64).
You can eyeball the numbers from the in-game graphs or read off the exact numbers for engine economy and power from the Results/Curves section of the engine variant .lua file - example:
Results={
AdjustedAFR=12.75,
AverageCruiseEcon=453.43594397352001,
BaseEcon=338.99330784286002,
BaseTorque=293.31209796106998,
BaseVE=0.93100000000000005,
CoolingRequired=88.864391049931996,
Curves={
...]
{
6500, -- <-- this is the engine RPMs
199.28471402951001,
135.65301510020001, -- <-- this is the power in kW
523.85505501344005, -- <-- this is the economy in g/kWh
23.536122865397001,
RPM=6500
} --[table: 0x0f26e668]],
...]
PeakPower=135.65301510020001,
PeakPowerRPM=6500, -- <-- this is the RPMs for peak power (i.e. the RPMs to check in the Curves, above)
...]
To get fuel tank size, open the Trim .lua file, search for “Footprint”, multiply the dimensions, divide by 10000 (m^2/cm^2), and multiply by 7.
(Using the most pessimistic estimates, my car’s race fuel consumption would be 118.5 kg - one pit stop on a 61.2 kg tank.)