Maximum number of units globally

Hi,

It depends of what you want exactly.
If you want to set a global maximum order quantity, you could just create a limit via the menu Products>Limits :
www.hikashop.com/support/documentation/293-limits-tutorial.html
Note that this means that the customers will only able to add that amount of products to the cart. It's global to all the products, so if the limit is set to 1, the customer can add product A with a quantity of 1. He won't be able to add more quantity of that product, but he also won't be able to add any other product to the cart at all.
If you want to be able to have product A with a quantity of 1, and product B with a quantity of 1, and product C with a quantity of 1, then a limit is not the solution.
In that case, you need to set the maximum per order in each product.
However, you don't have to do it manually for each product. You can create a mass action with an action "update the values" on the "product_max_per_order" column with the value you want as maximum. When you click on the "process" button, it will set it for all the products at once.
Note that you can see there is a limitation of 500 in the massaction. So, if you have more than 500 products / variants, you can increase it to a few thousand elements max, or process the massaction several time, changing the starting value each time.
You can read more about mass actions here:
www.hikashop.com/support/documentation/167-massaction-form.html