I was asked to do a wedding cake with the base layer filled with cookie and cream filling. Do I need to refrigerate the cake after filling up until the reception?

Nope. Just fold crushed chocolate cookies into your standard buttercream. Voila!

I would use Bettercreme or Frostin Pride to make the filling. It doesn't require refrigeration up to five days and it's not as sweet as butter cream. I use it in place of whipping cream to make a mousse. Two cups non dairy frosting and one small box instant pudding whip until peaks form and fold in cookies. I have also used the cookies and cream pudding it was really good.