The Courtesy lights are on fuse F2.7(15a) in the Central Junction Box (CJB). The map reading lights under the mirror, the trunk release, and the trunk light are on the same fuse. Therefore, if the other things work, then the fuse has to be good.
If the “door ajar” dash warning light comes on, this proves that the door switches work.
There is a switch on the over head courtesy light. However, this is to turn it on.
There is always the possibility of something else being wrong. The overwhelming odds favor a bad bulb. It simply doesn’t make any sense to do any other tests until the bulb has been checked.
On the clutch, the Mustang has a quasi self adjusting clutch. Simply lift the clutch pedal. Use your foot or a hand. This releases the prowl holding the quadrant. You may hear a few clicks. Depress the clutch pedal. This will reset the throw out bearing free play. The free pedal travel does need to be reset from time to time as the clutch wears.
Many people find the Mustang clutch engages too high in the pedal travel for their liking. This is because of the self adjusting nature of the set up. The adjuster maintains a constant light pressure on the throw out bearing essentially setting the pedal free travel to near zero. The stock set up works fine for daily driving. Often it is enough just to know that is how it works coming from the factory.
The life of a clutch varies widely depending upon the driving habits of the owner. Things like resting your foot on the clutch, setting at lights for long periods of time with the pedal pushed in, quick starts with lots of slipping, lots of high RPM dumps, failure to keep adjusted, driving through high water, city driving, can decrease the life of a clutch. While it is possible to get a lot more than 100k miles on the factory clutch, many will not make it that far.
Other clues that you need a new clutch include chatter as the clutch is released. Slipping once in gear especially after a long trip (RPMs increase), burning smells, way too easy to pull away without bucking, very light pedal pressure, all possibly mean a weak clutch.
Welcome aboard. Good luck.