If you get 12v 3mm leds then they go straight in.(they have a built in resistor. Those are the kind I used.
Normal 3mm leds need the resistor adding
Some of the smaller switches have two leds in them one for illumination one for the on/off indication.
Not sure on the clock/oiltemp as they are different according to age of car. If it is a later Tf I believe they are the same led.
Earlier, they are a T5 bulb and a BA7s bulb