Get management software for them. Apple provide no program, just API hooks for others to build upon. Meraki have a cloud product we trialled and it seems good enough for most.
Don't set them up with individual accounts. This is a recipe for disaster - forgotten password, no way to distribute new apps to them. Set them up with a single apple account, with a very strong password. The using your management software you can push out bulk-purchased apps to all ios devices.
Disable installing apps if they have data cards (wifi only, your choice) - otherwise they can install YouTube and rip through 40gb of LTE data in a month causing massive bill shock.
If they have SIM cards, consider speaking to your provider to organise having your SIMs terminate at your end of a provider-level VPN. This way you can apply your corporate web policies on the devices and monitor usage (this will not work for iPads on wifi).
Prepare to replace them. We have software on about 500 iPads and Id say in 3 years, 50% have been replaced due to misuse (dropped into water, smashed, given to the kids) or warranty failures. No excess business insurance helps here.