Planning a 25th bday party for fiance*HELP*?

My fiance will turn 25 on the 25th of Sept (golden birthday). He never really had any big party's growing up so I am planning a BIG bash for him. I need help. It will be outside in our backyard. I live in WI. The weather might not permit and my house isnt big enough to fit all the guests. Anyway-his favorite colors are green silver and black. I bought tablecloths, tableware in those colors. i was planning on getting some balloon bouqets as well. What food should i serve? What other decorations-games-activites should i have? im getting a keg and our friends family and some small kids will be there. he wants to play beer pong with his friends but what should the rest of the guest do? Im planning on playing music also. new to the party planning.