Assuming that there will be four people attending the party, about one-sixth of a pound of grilled kielbasa per person should suffice.  This is approximately 4 ounces or 112 grams for each person, which is enough to make sure everyone can enjoy a few slices of the delicious smoked sausage.  To get an even better flavor, try marinating the kielbasa overnight in some olive oil, garlic, and herbs before grilling it.  That way, each bite will be packed with robust, smoky flavor and aromatics.