To control the setting of the passcode, you need to step up to an mdm. [ I'm 95% sure that an mdm can control the password setting. ]
You either to have your devices bought with dep enabled or use apple's configurator 2. Both approaches let you supervise the ipad. meraki is a free mdm.
Alternatively, you can can setup a master ipad. Make a copy of it. Then download the copy to another ipad. This is called cloning. Ask around perhaps someone is already supervising and cloning ipads you could tack onto. Apple configurator 2 supports cloning. See the last paragraph.
I'd see if you can find a student aid to help you out. As for a cheap experimental device, the iphone 4s runs the latest ios software. The iphone and ipad are functionally equivalent with the exception of the built in phone app on the iphone.
"This document offers guidance on some important considerations for getting the most out of your iOS deployment." Covers: Prepare your infrastructure. Set up devices. Configure and manage devices. Deploy apps and content. Plan for support.
https://www.apple.com/business/docs/iOS_Enterprise_Deployment_Overview.pdf
Quick overview of zero touch deplayment
http://www.apple.com/education/it/dep/
Consider DEP, Device Enrollment Program. Use VPP, Volume Purchase Program. Select an MDM, Mobile Device Management. Read the Google doc below and nsdjoey write up.
Overview of ipad & iphone deployment.
It's education focused.
http://www.apple.com/education/it/
Writing you own app for your business:
https://developer.apple.com/enterprise/
MDM -- Mobile Device Management
https://developer.apple.com/videos/play/wwdc2015-301/
For a comparison see this page:
http://www.enterpriseios.com/wiki/Comparison_MDM_Providers
VPP -- Volume Purchase Program
http://www.apple.com/business/vpp/
http://www.apple.com/education/it/vpp/
Using Apple Configurator 2
See ccsdtech writeup on page 5
See weinsteinbevit plus Meraki MDM on page 5
https://discussions.apple.com/thread/7302890?answerId=29798579022#29798579022&tstart=0#29798579
R