Is it appropriate to do a picnic themed engagement celebration?

Hello, my fiancé and would like to invite our family over for a engagement celebration in our huge backyard. We have a huge backyard. We both have big families, in total toys going to be about 35-40 people. We are going for a simple evening to remember gracefully. What do you guys think of this?
Is it appropriate to do a picnic themed engagement celebration?
Is it appropriate to do a picnic themed engagement celebration?
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