I have only limited experince myself in Xingyiquan but I spend the majority of my time in training Santi shi these days.
I have been taught the 5 elements, the five elements cascade form and I was shown the 12 animals by my first sifu but I currently only remember 2 of the animal forms one being Tiger and the other I know the form but I cannot remember the name.
When I practiced Wuxing and when I practiced in in the past I would train each one seperatley first. Actually that is how my sifus taught me as well and always in this order
Piquan, (chopping fist) - metal
Zuanquan, (drilling fist) - water
Bengquan, (crushing fist) - woo
Paoquan, (cannon fist) - fire
Hengquan, (horizontal fist) - earth
I tend to focus on Piquan first and work with that for a week or two and then work with Piquan and Zuanquan for a while and then Piquan, Zuanquan and Bengquan and so on until I am back at all 5 but the one I add I spend more time on. After that I work on the linking form. But as I said I am currently focusing on Santi shi. I brought just about every part of my internal CMA training back to the root. After I am comfortable (and happy) with my training at that level I will move on. And in Xingyiquan that means moving on to Piquan first.