There is no limitation on how many devices you can install the enterprise app. All you need is properly configured provisioning profile and signing identity and the UDID in the provisioning profile. I do believe you can distribute ad-hoc similarly as with normal iOS developer account, even easier.
There is much information available on StackOverflow already:
- IOS Enterprise Distribution Through OTA
- Enterprise distribution of iOS applications
- iOS Developer Enterprise Program
- iOS Enterprise Deployment / Expiration
- iOS enterprise account for distribution
- iOS Enterprise Developer Program
- Deploying ios apps wirelessly .Enterprise apps
And many more: https://stackoverflow.com/search?q=ios+enterprise
Please read through those first and you will get most of the information you need.