how do I download apps to multiple ipads upon purchase

Hi. Alternatively, if all the iPads are using the same Apple ID, enable Automatic Download of Apps in Settings > iTunes & App Store on the devices. Then, apps bought on one device will be automatically installed on the others. It will be done in the background, like app updates.

Are you using Family Sharing, or are you referring to an educational or work related setup? If you are talking about large group setup, those are handled by MDM software.