To establish audio content needs, it's important to understand a few things about how to best support gameplay when it comes to movement sounds. You can easily create a simplified step system, but a varied system produces a better experience. The importance of varied footstep sounds in a game can be a delicate balance of finding the right places to put resources without ending up with a system that uses up all of the available memory.
Think about the following questions to help you determine how extensive the footstep system should be:
How many step types will characters have? (Walk, run, scuff, turn...)
How many surface types need to be represented with sound? (Dirt, stone, sand...)
How will footstep sounds be triggered? (Animation, programatically...)
How often will you hear footsteps for an extended period of time? (2-5 minutes, 10-20 minutes...)