13 is convenient because most Arduino's already give you an LED connected to pin 13 through a series resistor, meaning you can upload the code to the board without adding any hardware. You're welcome to use whichever pin you like; you aren't tethered to pin 13.
Do you mean one after another? All at the same time? Binary counter? Random? The answer is yes to all, but the implementation is different
Look, I got it. You don't want to help me, but there are others that are willing to so please if all you want to do is continue down this road, save yourself some time and don't respond at all.
Everything that I try gives me an error.