I've reloaded revolver ammunition as many as 35 times. The case mouth gets small splits, from being belled and then crimped. But 9mm doesn't get nearly so much of a crimp, just a taper crimp. No reason you couldn't get 20+ reloads. Odds are, you'll lose the brass, before you wear it out.
I color code the case heads of my 9mm reloads with a permanent marker. One time reloads get colored green, 2 to 5 times gets blue, and when they start getting beat up, I color the case heads black.
At most ranges you can pick up plenty of 9mm brass. As I pick up brass, I sort it into small paper bags by the color of the case head, and 'new' 9mm range brass gets thrown into its own bag. Saves a lot of time later. I use the small paper bags sold for taking lunches to work, to sort the brass into.
Load your 9mm just powerful enough to reliably cycle your pistol(s). It saves wear and tear on your gun(s).
In the mid 1970's, when I started reloading 9mm, I cast my own bullets, and even with the cost of scrap lead, bullet lube, everything, i could reload a box of 50 9mm for almost exactly $1/each. I used to shoot 700 rounds a week. I spent ALL my free time casting bullets, sorting and sizing them, and reloading. I put over 30,000 rounds through a S&W Model 59. In hind sight, I wish I had used a better lube on the slide rails; I just used gun oil. Grease is better for so much shooting, especially for a gun with an aluminum frame. It got fairly worn, but I got more in trade for the Model 59 than I paid for it, when I traded for a 659. Good times.
I love the 9mm round. So many cool firearms chambered for it. It's the cheapest centerfire ammunition to reload, as well.