when to use a yeast starter.

I am going to do a beer with OG of 1.049. when I select the starter tab it says I need 196.5 billion cells using Wyeast 1098.
If I  do a yeast starter with a stir plate the starter would have 237.8 billion cells.
  Is that over pitching? And so how much is too much over what is recommended by the BeerSmith software?

Check out the starter size. You can change the yeast starter size. Adjust that to match cell count for your brew. I also recommend a yeast nutrient at about the 10 minute mark in the boil.