Lauren.
Some of those problems are symptomatic of a failing battery, so I suggest you get it professionally tested before doing anything else. By that I mean a deep discharge test, not a multimeter voltage reading, at an auto electrician or independant Audi specialist.
The tester should provide you with a printed report of the battery condition, which at six years old is well past its sell by date. If he does not give you a printed report he has not done the test properly and you should go elsewhere. Some folk recommend Halfords for this job; I do not.
If a new battery is required ensure the fitter codes it to the car. Once you have a reliable stable power source from the battery you may find other faults disappear, but even if they don't, only a good battery will give sensible answers in any further diagnosic tests.