[Nonfractal]

What’s the best way to wire them up? To the motor, or from the guide area? 

For a regular analogue car, it should not matter whether you wire to the guide or to the motor. 
The only considerations are tidiness and stress on the wires . Best select a connection point that does not move about too much. 
You might even consider splicing the led wires into the middle of the power wires. 
Did you chose a  connector to use? The lights will be in the body and the connection will be somewhere on the chassis so you will need a connector for the time you lift the body off the car. 

Digital cars run a fixed voltage the the guide and the onboard chip to drive the motor. 
If the light chip is oxigen, and you have slot it light rig,  plug right into the onboard chip.
A simple light rig (no brake light etc) wire the lights to the front ofthe chip (between chip and guide) so that the lights are on whether car is on track but Stationery) 
If the light circuit has brakes (bright red leds) and maybe even an exhaust flash, you have to wire it to the motor.

Voltage dropping 
I have wired circuits without resistors. This can be done by wiring all four or five leds in series. If they need 3v each this works well.
However, series circuits mean that one led failure knocks out all of the lights.

Parallel wiring is more reliable but does require (at least one) resistor. 
Use ohms law to figure that out volt = amps x resistance 
You'll need to know how current that the leds draw. 
Alternatively, sellers often offer suitable resistors.

Alan