You need to flesh out the menu. I strongly suggest an appetizer table for the hour after the wedding while you do pictures; for 300, you need 3 stations, and the usual is 3 items (such as a cheese platter with crackers, a fruit platter, and one or two dips and spreads plus bread or crackers, plus one or two punches- 2 if one is alcoholic). This is critical if there are children among the guests.

Also for 300 people, you need 5-6 serving lines, can be 3 two sided; at least 4 people in the kitchen; and at least 18 other staff to set up, serve and clean up the party. Separate beverage, salad and dessert stations. Your mom can't be the kitchen manager if you want to have her near you on the big day.

You need to add bread to the menu. Some of the lasagna needs to be meatless; with 300 guests you will have some vegetarians.