I know in iOS developer program, a developer can use an ad hoc distribution profile to build an app, and this app is for testing purpose and can be installed on up to 100 de
Beginning iOS 9, another important consideration is on first install Apple prompts you with an 'Untrusted Enterprise Developer' prompt. This requires you to go to Settings: General > Profiles and select 'Trust X' for the correct profile.
Not a show stopper. However, an important consideration if you need to do a large distribution as testers need to be informed.
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:
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.