I wanted to know how to configure a job so that it will have max n instances running all the time. I have tried running my job every 5 mins and job option is set to "run anyway" but that schedules lot of job in parallel.
You can set up a job with only the beginning time, let's say midnight - no end time then in Repeats you can select Rerun same occurrence and Repeat every n minutes (do not specify # of times). This will run starting at midnight, every 5 minutes, n times until 11:59 pm. I hope this is what you're looking for.