How's the planning coming along? It's so fun having parties for the little ones.
Looking back on all the crazy, obsessive/compulsive, over-the-top things I did, I wish I could tell my younger self, "Don't stress over it!"
The kids are happiest with familiar foods (PBJs, cheese sandwiches, chips) and the adults want to see you have a good time and interact with them. I wouldn't (now) even attempt a "build your own" food bar for four-year-olds, but just have toy trucks in the background of the food table.
One thing we did that worked great (and eliminated frantic ice cream scooping during the party) was to buy flat bottomed ice cream cones, scoop vanilla ice cream into them and place them in pans in the freezer. Everyone who wanted ice cream with their cake had a pre-portioned scoop with no hassles.