Do I need to do anything at the base to support deck steps?
If you want to land on grass you need footings below the frost line in Iowa.  Just two at the bottom.

The other option is to put in a solid stone or concrete pad.  Needs to be on compacted soil with gravel under.  Most importantly it needs to be level.  Note that this does not officially meet code but I have never seen a deck not pass if doing this.

To clarify on what an inspector would want in a pad - it needs to run the width of your stairs, the stair bottoms should be resting firmly on pad (pad should probably extend out a few inches width wise), and pad should support a reasonable human step from the lowest step you create.  I have done this in your exact situations with a variety of large stone.  I think with a short stair case the only reason I wouldn't do it is if the soil is disturbed.