Easiest way to generate incrementing number is using Add > Logic Element > Count and set the counter initial value followed by maximum value also set the reference name.
You can access the reference name by providing ${reference name} in the request.
Generating unique random
Go to Add > Pre processor > User Parameters
Enter the parameter name which you want to have it unique and assign this method to generate unique number to${__V(${__Random(30002,40000,)})}
If you want to generate unique string, 
You can also generate number in incremental order using Bean Shell scripting Add > Pre processor > BeanShell Processor.
Hope this helps.