iOS / iPhones in Enterprise: Deployment of App Store apps in batch
If the apps were purchased through the Volume Purchase Program, you can install them using Apple Configurator. Add the VPP codes, connect the devices and click install. Alternatively if the apps are free you can simply drag the app into the app list and install it that way.

For more information regarding this, see this Apple KB article:


Apple Configurator: Using Volume Purchase Program (VPP) Redemption Codes


Otherwise as you mentioned the Caching Server in OS X Server would cache a copy of the app so that downloads would come from your server instead of over the internet.