IPad Air to projector cord choice-sound airport Express?

Ok so I'm looking to use my ipad to play movies in the back yard for the kiddos.

The projector I am going to order has VGA and HDMI ports.

I am looking to project the movie to the screen/projector

through one of these ports and then stream the sound through my airport express which connects to the backyard speakers I have using airplay.

Does it matter which cord I use to connect to projector? I was wondering since hdmi has sound as well but I want to use the airport express for this.

Does anyone have advice on wether this is the best setup? I want to make sure it will all work before investing the money. THX