Training staff was done right after learning Tui Shou but before learning shorter weapons in one school I have trained in. The staff, I was told, was the "first weapon" and learning the staff would lead to a greater understanding of Taijiquan.
After several years of staff training, I don't know that I found any greater understanding of Taijiquan but I did enjoy what I was doing quite a bit.
When I finally did begin to train saber I don't know that learning some staff first brought any particular insights but I did have more flexible wrists because of it and that helped quite a bit.
It was not until many years later that I began to train sword (Audi should remember the first day I ever took a sword lesson, he was there
). Again, I did not have any brilliant insights into sword given to me by my time swinging around a big piece of wood.
I don't know if my experience helps any with this discussion or not. I just figured I'd throw it out there to let Taijisufi know that not everyone benefits greatly from training staff before the shorter weapons.
Audi's advice is quite sound, I think. I agree that it would be best to stick with smaller, lighter weapons if you have injuries to your hands or forearms.
Trust me, a staff becomes very, very heavy quickly during a staff routine. It takes quite a bit of mental effort and not an inconsiderable amount of physical effort to keep your movements from your center when eight feet of hardwood changes where your center is quite dramatically every time you move it.
Maybe that's the "greater understanding of Taijiquan" I was told would come about; holding your center in changing circumstances. A good lesson but...
If you do greater injury to your hands while doing staff, which in my experience seems likely, you may learn the lesson but you will not be able to continue practicing it or anything else for very long.
On another note, there is no need to strengthen the arms or condition your body before beginning Tui Shou. In my experience the more stiff muscle you have the greater obstacle you have to overcome before you can begin to develop listening jing.
And you really want to develop listening jing.