The program at the end of the array list and cycles towards the first item. I learned that this is the "good" way to use an array list. Is it okay at some times to start from 0 and count upwards?
Yes, it's actually preferred in most cases. Backwards iteration is a micro-optimization that only applies to certain programming languages. I seem to recall that Java is one language where backwards iteration is said to be faster, but I couldn't tell you if that's the case for Processing.
My position: use forward iteration until you have a demonstrated need to use backwards iteration. Don't optimize individual lines of code until it works and your profiling tells you that it will be worth it.