Sorry for the late reply.
On the iPad, turn off automatic app downloads and automatic updates in the App Store settings. Turn off music, videos and books whilst you're there. Install Mac OS X Server from the App Store on your main mac. Turn on caching (there's a tutorial in the app that enables you to do this). On iTunes, enable automatic updates and automatic downloads.
At most, you'll then be downloading an app twice from an outside source. Once to the device that requests it, once to iTunes (since it's automatically downloading the apps requested on the account it's logged in to).The rest will just get them from the server. Nice, huh? Low cost too since the server software is so cheap.
If you want to wirelessly push out apps from the mac to the iDevices rather than requesting them from each device, just use Apple Configurator too. Made to control and set up groups of iPads. Very handy and it's free. It's on the Mac App Store.