Just wanted to share my experience with both processing with java and python.
I started Processing with Java, and used it for quite a long time before I switched to Python. The reason being is that prototyping visual ideas came to me faster in python, and in many ways it almost started to feel like a creative writing exercise. This is facilitated by usefuls ways of dealing and transforming lists with list comprehensions, unpacking, other built-in functions and useful standard modules. Compare that with processing with java, where it’s watered down to make it less verbose, but you still have to write more lines of code to achieve what could be expressed in much fewer lines in Python. Writing fewer lines of code is important to me because it enables me to focus on the higher level aspects of the visual idea. On the other hand, Processing with Python tends to be slower than processing.java, but not to the point where it hinders my creative output. Sometimes I port my sketch to java if I felt the need for a faster sketch.
I don’t know if you should start processing with python immediately, because I haven’t done that. Even though most learning resources would be made for processing.java, I think one could start immediately with processing.py, and people here try their best to answer people’s questions for processing.py here.